url stringclasses 71
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http://lib.ysu.am/disciplines_bk/ea4b336028cd91ba7265865d8fde153c.pdf | ea4b336028cd91ba7265865d8fde153c.pdf | true | 519 | Solutions for Chapter 26 – The aldol and Claisen reactions
267
PROBLEM 7
The synthesis of six-membered ketones by intramolecular Claisen condensation
was described in the chapter where we pointed out that it doesn’t matter which
way round the cyclization happens as the product is the same.
N
EtO2C
CO2Et
Me
1. E... |
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Solutions Manual to accompany Organic Chemistry
Though these compounds are different, each gives the same ketone after
hydrolysis and decarboxylation as the ketone carbonyl group is on the same
position in the ring in both compounds.
PROBLEM 8
Attempted acylation at carbon often fails. What would be the act... |
http://lib.ysu.am/disciplines_bk/ea4b336028cd91ba7265865d8fde153c.pdf | ea4b336028cd91ba7265865d8fde153c.pdf | true | 519 | Solutions for Chapter 26 – The aldol and Claisen reactions
269
R
CHO
R
CHO
R2NH
Me3SiCl
Et3N
R
NR2
R
OSiMe3
enamine
silyl enol ether
MeCOCl
MeCOCl
TiCl4
R
CHO
O
R
CHO
O
The enolate formation in the second example is a separate step and will
work well because the two carbonyl groups cooperate in forming a stable
e... |
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Solutions Manual to accompany Organic Chemistry
PROBLEM 9
Acylation of the phenolic ketone gives compound A, which is converted into an
isomeric compound B in base. Cyclization of B gives the product shown. Suggest
mechanisms for the reactions and structures for A and B.
OH
O
PhCOCl
pyridine
C15H12O3
KOH
C... |
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271
OH
O
Ph
O
H
O
O
Ph
OH
H
O
O
Ph
OH2
O
O
Ph
H
O
O
Ph
O
O
Ph
PROBLEM 10
How could these compounds be made using the acylation of an enol or enolate as
a key step?
O
CO2Et
O
CO2Et
Purpose of the problem
Practice in using acylation at carbon to make... |
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Solutions Manual to accompany Organic Chemistry
CO2Et
LDA
EtO
OLi
EtO
OSiMe3
Cl
O
O
CO2Et
+ TiCl4 if
silyl enol ether
is used
or
LDA
Me3SiCl
Route B requires the synthesis of the ketone starting material and this
could be done by Grignard methods (chapter 9) or by acylation of an
organo-copper compound with ... |
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273
The second example might just go with simple base (MeO–) catalysis as
the conjugated ketone enolate is much more stable than the enolate of the
ester. However, it’s probably safer to use a lithium enolate (or a silyl enol
ether—though you’d then have t... |
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Solutions Manual to accompany Organic Chemistry
Suggested solution
Only the diester can form an enolate and ethyl formate (HCO2Et—it is half
an ester and half an aldehyde) is much more electrophilic than the diester.
We should expect the diester to be acylated by ethyl formate.
EtO2C
CO2Et
EtO
EtO2C
O
OEt
H
... |
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Suggested solutions for Chapter 27
PROBLEM 1
Suggest a mechanism for this reaction, commenting on the selectivity and the
stereochemistry.
O
SMe2
1. t-BuOK
2. Raney Ni
EtOH
O
Purpose of the problem
The opportunity to explore the consequences of the intramolecular version
of an important reaction.
Sugges... |
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Solutions Manual to accompany Organic Chemistry
PROBLEM 2
Explain the regiochemistry and stereochemistry of this reaction.
Br
O
Me2S
CO2Et
+
O
Br
H
EtO2C
Purpose of the problem
Exploration of sulfur ylid chemistry.
Suggested solution
The ylid is stabilized by conjugation with the ester group—you can think ... |
http://lib.ysu.am/disciplines_bk/ea4b336028cd91ba7265865d8fde153c.pdf | ea4b336028cd91ba7265865d8fde153c.pdf | true | 519 | Solutions for Chapter 27 – Sulfur, silicon and phosphorus in organic chemistry
277
PROBLEM 3
Give mechanisms for these reactions, explaining the role of sulfur.
O
OMe
OMe
SH
SH
HCl, CHCl3
S
S
S
S
1. BuLi
2. MeI
3. BuLi
S
S
S
S
HgCl2
H2O
acetone
O
O
Br
4.
Purpose of the problem
Sulfur acetals as good nucleophil... |
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Solutions Manual to accompany Organic Chemistry
H
S
S
OH
OMe
H
S
S
O
H
etc
S
S
S
S
continued...
Now the sulfur atoms work to stabilize an anion (organolithium) formed
by deprotonation. Alkylation and hydrolysis with a mercury catalyst gives
the product.
S
S
S
S
S
S
S
S
Li
2. MeI
S
S
S
S
Me
3. BuLi
S
S
S
S
... |
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279
Suggested solution
The first reaction is a straightforward cyclopropane formation with a
sulfoxonium ylid and a conjugated ketone. The only unusual feature, the
MeO group, makes no difference.
Ph
Ph
O
OMe
SMe2
CH2
O
Ph
Ph
O
OMe
SM... |
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Solutions Manual to accompany Organic Chemistry
Ph3P
1. NaNH2
Ph3P
2. i-PrCHO
Me
H
Me
H
H
Me
δ 0.95
δ 0.95
δ 2.65
δ 1.60
δ 5.35
δ 5.10
J 7
J 4
J 5
J 10
PROBLEM 6
A single geometrical isomer of an insect pheromone was prepared in the
following way. Which isomer is formed and why?
MeO2C
CHO
Ph3P
CHO
MeO
Me... |
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281
PROBLEM 7
How would you prepare samples of both geometrical isomers of this compound?
HO
CO2H
Purpose of the problem
A simple stereocontrolled alkene synthesis but both isomers are needed.
Suggested solution
There are many metho... |
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Solutions Manual to accompany Organic Chemistry
PROBLEM 8
Which alkene would be formed in each of these elimination reactions? Explain
your answer mechanistically.
R1
R2
Ph3P
OH
base
R1
R2
PhSO2
OAc
Na/Hg
R1
R2
Me3Si
OH
base
R1
R2
Me3Si
OH
acid
?
?
?
?
Purpose of the problem
Revision of the three main meth... |
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283
The Peterson reaction is a syn-elimination under basic conditions, giving
the Z-alkene from this starting material, but an E2 anti-elimination under
acidic conditions, giving the E-alkene from this starting material.
R1
R2
Me3Si
OH... |
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Solutions Manual to accompany Organic Chemistry
PROBLEM 10
Give mechanisms for these reactions, explaining the role of silicon. Why is this
type of lactone difficult to make by ordinary acid- or base-catalysed reactions?
EtO2C
Cl
O
Me3Si
MgCl
EtO2C
SiMe3
OR
OR
+
O
O
Lewis acid
Purpose of the problem
Basic o... |
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285
PROBLEM 11
How would you carry out the first step in this sequence? Give a mechanism for the
second step and suggest an explanation for the stereochemistry. You may find
that a Newman projection helps.
O
CHO
?
O
SiMe3
O
EtAlCl2
... |
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Solutions Manual to accompany Organic Chemistry
on the allyl silane tucks underneath the six-membered ring while the double
bond of the allyl silane projects out into space to give the stereochemistry
found in the product. The ratio between this diastereoisomer and the other
varies from 2:1 to 7.5:1 depending ... |
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287
Suggested solution
We’ll approach this as a spectroscopic problem, rather than predicting the
outcome and then making the data fit. First analyse the data, measuring
chemical shifts, integrals and J values.
δH ppm
integral
mult... |
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Suggested solutions for Chapter 28
PROBLEM 1
How would you make these four compounds? Give your disconnections, explain
why you chose them and then give reagents for the synthesis.
H
N
H
N
NO2
O2N
MeO
O
S
Purpose of the problem
Exercises in basic one-group C–X disconnections.
Suggested solution
We wish ... |
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Solutions Manual to accompany Organic Chemistry
H
N
NO2
O2N
C–N
nucleophilic aromatic
substitution
NH2
NO2
O2N
Cl
+
Cl
NO2
O2N
Cl
HNO3
H2SO4
i-PrNH2
H
N
NO2
O2N
analysis
synthesis
For the ether we again have a choice from two C–O disconnections. We
prefer not to add the t-butyl group by SN2 (though we could by... |
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291
Suggested solution
There are obviously more choices when you use C–C disconnections, but
choose wisely! We suggest a solution, but you may have thought of others.
The first compound is an alkyne and disconnection next to the alkyne (but
not on the side of the... |
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Solutions Manual to accompany Organic Chemistry
Suggested solution
Both compounds have two oxygens singly bonded to the same carbon atom:
they are acetals so they come from a carbonyl compound. Disconnecting the
acetals helps us see what we are really trying to make.
OH
OMe
MeO
1,1-diX
1,1-diX
acetal
acetal
... |
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293
O
CO2Et
OEt
O
CO2Et
OEt
CO2Et
O
CO2Et
O
CO2Et
O
Disconnection A
Disconnection B
The advantage of disconnection B is that the synthesis involves a simple
self-condensation of ethyl propionate. Methylation of the resulting keto-
ester followed by reduction to t... |
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Solutions Manual to accompany Organic Chemistry
PROBLEM 4
Propose syntheses of these two compounds, explaining your choice of reagents
and how any selectivity is achieved.
O
O
O
Purpose of the problem
First steps in designing syntheses in which selectivity is required.
Suggested solution
The first compou... |
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295
O
O
C–O
ester
OH
CO2H
redraw
1
2
4
3
5
HO2C
OH
We discover that we have a 1,5-relationship between the functional
groups and so we shall need conjugate addition. We must change the
alcohol into a ketone, and the acid group to an ester. Notice that there are ... |
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Solutions Manual to accompany Organic Chemistry
PROBLEM 5
The reactions to be discussed in this problem were planned to give syntheses of
these three molecules.
Ph
O
CO2Me
O
O
1
2
3
In the event each reaction gave a different product from what was expected, as
shown below. What went wrong? Suggest synthese... |
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297
that occurred is the Darzens condensation. To avoid this problem use a
specific enolate of the ketone such as an enamine or a β-ketoester.
Cl
CO2Me
Cl
OMe
O
O
CO2Me
Cl
O
CO2Me
O
O
R2NH
R2N
Cl
CO2Me
aqueous acid
work-up
CO2Me
O
target 2
MeO
MeOH
In the third... |
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Solutions Manual to accompany Organic Chemistry
PROBLEM 6
The natural product nuciferal was synthesized by the route summarized here.
BrMg
O
O
?
OH
O
O
?
CHO
?
CHO
(a) Suggest a synthesis of the starting material.
(b) Suggest reagents for each step.
(c) Draw the retrosynthetic analysis giving the discon... |
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299
(b) The Grignard has obviously been added to a ketone to give the tertiary
alcohol, but how do we replace OH by H? One way is direct catalytic
hydrogenation but an easier way is to eliminate the tertiary (and benzylic)
alcohol and hydrogenate the alkene. The ... |
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Solutions Manual to accompany Organic Chemistry
PROBLEM 7
Show how the relationship between the alkene and the carboxylic acid influences
your suggestions for a synthesis of these three compounds.
CO2H
CO2H
CO2H
Purpose of the problem
An exploration of the importance of functional group relationships.
Sug... |
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301
analysis
synthesis
CO2H
FGI
CO2Et
C–C
CO2Et
CO2Et
Br
CO2Et
CO2Et
1. EtO
Br
2.
CO2Et
CO2Et
1. NaOH, H2O
2. H , heat
CO2H
PROBLEM 8
How would you make these compounds?
H
N
OH
CO2H
NH2
Purpose of the problem
A reminder of reductive amination and that simple ... |
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Solutions Manual to accompany Organic Chemistry
analysis
synthesis
OH
C–C
CHO
BrMg
+
FGI
Br
Br
1. Mg, Et2O
2. HCO2Et
TM
Br
1. Mg, Et2O
2. RCHO
TM
R =
cyclohexyl
or
The carboxylic acid could be made by double alkylation of malonate or
some other specific enol equivalent.
analysis
synthesis
CO2H
C–C
alkylation... |
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303
Purpose of the problem
An exercise in counting to reinforce the way that odd and even relationships
affect the choice of a synthetic route.
Suggested solution
The three diketones have 1,3-, 1,4-, and 1,5-dicarbonyl relationships. In each
case the obvious dis... |
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Solutions Manual to accompany Organic Chemistry
O
R
O
analysis
synthesis
O
R
O
1,5-diCO
specific
enol(ate)
equivalent
needed
O
CO2Et
1. EtO
2.
R
O
O
R
O
CO2Et
1. NaOH
2. H , heat
target molecule
PROBLEM 10
A synthesis of this enantiomerically pure ant pheromone was required for the
purposes of pest control... |
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305
O
analysis
synthesis
C–C
alkylation
specific
enolate
equivalent
needed
Br
+
O
O
NaOEt
CO(OEt)2
O
EtO2C
1. NaOEt
2. RBr
O
CO2Et
O
H+, H2O
target molecule
|
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Suggested solutions for Chapter 29
PROBLEM 1
For each of the following reactions (a) state what kind of substitution is suggested
and (b) suggest what product might be formed if monosubstitution occured.
N
H
Br2
?
N
HNO3
H2SO4
?
S
MeCOCl
SnCl4
F
N
F
?
MeO
?
Purpose of the problem
A simple exercise in arom... |
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Solutions Manual to accompany Organic Chemistry
The last reaction is a nucleophilic aromatic substitution on a pyridine. It
occurs only at the site where the negative change in the intermediate can be
delocalized onto the nitrogen.
F
N
F
OMe
F
N
F
OMe
F
N
OMe
PROBLEM 2
Give a mechanism for this side-chai... |
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309
PROBLEM 3
Give a mechanism for this reaction, commenting on the position in the furan ring
that reacts.
O
OH
H
O
Purpose of the problem
An unusual electrophilic substitution on furan with interesting selectivity.
Suggested solution
Furans nor... |
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Solutions Manual to accompany Organic Chemistry
Purpose of the problem
Regioselectivity test with contrasted electrophilic aromatic substitution.
Suggested solution
In each case we have a choice between reaction on a benzene ring or an
aromatic heterocycle. The pyrrole is more reactive than the benzene and th... |
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311
PROBLEM 6
Suggest what the products of these nucleophilic substitutions might be.
NH2
Me
Cl
+
N
Cl
CO2Et
?
N
N
Cl
Cl
N
H
H
N
+
?
Purpose of the problem
Checking your understanding of nucleophilic aromatic substitution
involving decisions on c... |
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N
N
Cl
Cl
N
H
N
H
N
N
N
Cl
H
N
Cl
H
N
N
N
Cl
H
N
H
N
N
N
Cl
H2
N
PROBLEM 7
Suggest how 2-pyridone might be converted into the amine shown. This amine
undergoes nitration to give compound A with the NMR spectrum given. What is
the structure of A? Why is this iso... |
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313
The nitration occurs only because this pyridine is activated by the extra
amino group so you could start by predicting which compound might be
made. Alternatively you could work out the structure from the NMR. The
key points are (i) A has only three... |
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PROBLEM 8
The reactions outlined in the chart below were the early stages in a synthesis of an
antiviral drug by the Parke-Davis company. Consider how the reactivity of
imidazoles is illustrated in these reactions, which involve not only the skeleton of
the mole... |
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315
N
H
N
N
H
O
O
N
H
N
N
O
HO
N
H
N
ON
O
Ph
H
O
N
H
N
O2N
Ph
OH
Ph
OH
N
H
N
Ph
O2N
Next, alkylation occurs on one of the nitrogen atoms in the imidazole
ring. We need the anion of the imidazole which could be alkylated on either
nitrogen. Alkylation o... |
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PROBLEM 9
What aromatic system might be based on this ring system? What sort of reactivity
might it display?
N
Purpose of the problem
A chance for you to think creatively about aromatic heterocycles.
Suggested solution
The aromatic system has the poetic na... |
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317
Suggested solution
The allylic group evidently goes into the 2-position so deprotonation of the
starting material by LDA must occur there, directed by both the oxygen and
bromine atoms. The second electrophile (MeI) talkes the place of the Br
atom... |
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Suggested solutions for Chapter 30
PROBLEM 1
Suggest a mechanism for this synthesis of a tricyclic aromatic heterocycle.
N
NH2
Cl
O
+
base
N
H
N
Purpose of the problem
A simple exercise in the synthesis of a pyridine fused to a pyrrole (or an
indole with an extra nitrogen atom).
Suggested solution
The f... |
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PROBLEM 2
Is the heterocyclic ring created in this reaction aromatic? How does the reaction
proceed? Comment on the regioselectivity of this cyclization.
O
OH
HO
CO2Et
O
H2SO4
HO
O
Purpose of the problem
Exploring the synthesis and aromaticity of an unfamili... |
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321
PROBLEM 3
Suggest mechanisms for this unusual indole synthesis. How does the second
mechanism relate to electrophilic substitution on indoles (p. 746) ?
O
NNHPh
HCl
N
O
ZnCl2
N
H
N
O
Purpose of the problem
A combination of a Fischer indole synthe... |
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N
N
O
ZnCl2
N
N
O
ZnCl2
H
NH
N
O
PROBLEM 4
Explain the reactions in this partial synthesis of methoxatin, the coenzyme of
bacteria living on methanol.
NH2
NHCHO
OMe
1. HONO
2. KOH,
O
CO2Me
NH
NHCHO
OMe
N
MeO2C
HCO2H
80 °C
NHCHO
OMe
NH
MeO2C
HCl, H2O
Me2C=O
NH2
... |
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323
NH2
NHCHO
OMe
1. HONO
N
NHCHO
OMe
N
O
MeO2C
NHCHO
OMe
N
N
O
OH
CO2Me
H
NHCHO
OMe
NH
N
CO2Me
Now that we have the hydrazone, the Fischer indole step is
straightforward and gives the indole-2-carboxylic acid derivative. There is
only one site for an ... |
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PROBLEM 5
Explain why these two quinoline syntheses from the same starting materials give
(mainly) different products.
N
Ph
O
KOH, H2O
NH2
O
Ph
O
H2SO4, HOAc
N
Ph
Purpose of the problem
An exercise in regioselectivity in a heterocyclic synthesis controlled by... |
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325
PROBLEM 6
Give mechanisms for these reactions used to prepare a fused pyridine. Why is it
necessary to use a protecting group?
N
Me
Ph
O
O
O
+
HCl
dry Et2O
O
O
O
N
Me
Ph
H
NH2OH
HCl
EtOH
N
N
Me
Ph
H
Purpose of the problem
Saturated and aromatic... |
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The enol must attack the five-membered ring in a cis fashion as the tether
is too short to reach the other side. There is no control over one stereogenic
centre (represented with a wiggly line) but that is unimportant as it is soon
to disappear.
Now the reaction... |
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327
Purpose of the problem
Revision of aromatic nucleophilic substitution and a chance to unravel an
interesting mechanism.
Suggested solution
The first reaction forms A, just the enamine from the ketone and the
secondary amine (morpholine). Below we ... |
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C
HCl
EtOH
N
N
N
NO2
NH
O
N
N
N
NO2
H
N
N
N
NO2
NaOH
PROBLEM 8
Give detailed mechanisms for this pyridine synthesis.
OMe
CHO
O
O
KOH,
MeOH
25 °C
OMe
O
O
O
O
NH2OH
OMe
O
O
N
Purpose of the problem
Revision of aldol and conjugate addition reactions of enol(... |
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329
PROBLEM 9
Suggest a synthesis for this compound.
N
H
CO2Me
MeO
MeO
NHPh
Purpose of the problem
The synthesis of an indole with a slight twist.
Suggested solution
This looks very much like a perfect subject for the Fischer indole synthesis.
Let... |
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chloride that could be displaced with amines to give a series of anti-
depressants.
MeO
MeO
N
H
NH2
O
O
O
HCl
+
N
H
MeO
MeO
O
O
dry HCl
MeOH
N
H
MeO
MeO
Cl
CO2Me
PhNH2
N
H
MeO
MeO
NHPh
CO2Me
PROBLEM 10
How would you synthesize these aromatic heterocycles?
S
Ph... |
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331
bonds to give the thioamide and another α-bromoketone remembering to
let the nucleophiles exercise their natural preferences: sulfur attacking
saturated carbon and nitrogen attacking the carbonyl group.
analysis
synthesis
S
N
Ph
C–N + C–S
Ph
+
O
Br... |
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Suggested solutions for Chapter 31
PROBLEM 1
Predict the most favourable conformation for these insect pheromones.
O
O
OH
O
O
OH
Purpose of the problem
Practice at drawing the conformations of cyclic acetals.
Suggested solution
There are many good ways to draw these conformations and yet more not
quite so... |
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PROBLEM 2
The Lolium alkaloids have a striking saturated heterocyclic skeleton. One way to
make this skeleton appears below. Suggest a mechanism and explain the
stereochemistry.
N
O
NHMe
NH
O
Br2
N
O
Br
Lolium alkaloid skeleton
Purpose of the problem
Analys... |
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335
PROBLEM 3
One of the sugar components of the antibiotic kijanimycin has the basic structure
shown here and NMR spectrum given below. What is the stereochemistry? When
you have deduced the structure, suggest which conformation the molecule ... |
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and the stereochemistry: H5 and H6 are axial; H1 and H4 are equatorial. That
is why there are no large vicinal (3J) couplings to the diastereotopic CH2
group (H2 and H3). All couplings not shown on the second diagram are
<4 Hz.
O
H
MeO
H
Me
OH
H
H
H
OMe
H
O
H
M... |
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337
to get the two dotted lines in the transition state diagram at the required
180° to each other.
O
H
Ph
I
HO
Ph
I
(+)
(+)
O
I
Ph
Now what about the stereochemistry? Did you notice that each product
has an all-trans arrangement of substit... |
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the molecule into a chair a reasonable overlap between the required p
orbitals is possible.
2M HCl
N
H
H
O
O
H
N
CHO
O
=
imine
formation
N
O
N
OH
OH
–H
5-exo-trig
N
O
6-endo-trig
PROBLEM 6
Consider the question of Baldwin’s rules for each of these reactions. ... |
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339
NH
OH
MnO2
NH
O
=
NH
O
N
O
H
N
O
The second example is again 6-endo-trig but it is acid-catalysed:
protonation increases the reactivity of the enone and reduces its rigidity.
Both these 6-endo-trig reactions occur through chair-like trans... |
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Me
Me
O
Me
Me
Me
O
Me
H
H
H
H
H
H
H
δC 8.15
δH 1.00
δH 2.49
δH 5.99
δH 6.71
δH 0.90
16 Hz
7 Hz
7 Hz
7 Hz
7 Hz
δH 1.77 (m)
δH 2.09
δC 22.5
δC 42.0
δC 33.1
δC 131.8
δC 144.9
δC 28.3
δC 191.6
PROBLEM 8
Reaction between this aldehyde and ketone in base gives a compou... |
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341
that the two hydrogens on the same carbon are diastereotopic. In fact, the
expected conjugate additon of HBr to the enone has occurred.
HBr
A
OH
Br
O
Br
H
H
O
H
Br
H
H
B
The three hydrogens that we have drawn in form an ABX system: A and... |
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Solutions Manual to accompany Organic Chemistry
Suggested solution
The two isomers have cis and trans ring junctions so we should start by
making conformational drawings of both. The trans compound is easy as it
has a fixed trans-decalin shape. The cis compound can have two
conformations as both conformers ca... |
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343
Suggested solution
By NMR of course. Both compounds are six-membered rings so we should
first make conformational diagrams of all the possibilities. Both will have the
t-butyl group equatorial. The first compound can have the methyl group ... |
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O
O
t-Bu
O
O
O
t-Bu
O
O
O
t-Bu
O
Me
Me
Me
Me
Me
Me
HA
HB
HB
HA
HB
HB
HA
HC
HB
Me cis to t-Bu
Me trans to t-Bu
unsymmetrical compound
unsymmetrical compound
symmetrical compounds
NOE
PROBLEM 11
The structure and stereochemistry of the antifungal antibiotic ambruti... |
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345
PROBLEM 12
A reaction produces two diastereoisomers of the product below: isomer A has δH
3.08 (1H, dt, J 4, 9, 9) and 4.32 (1H, d, J 9), while isomer B has δH 4.27 (1H, d, J 4). All
other protons (except those of the Me groups) overlap i... |
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Conversion to A occurs by enolate formation and the trans compound is
more stable than the cis, as you might expect.
PROBLEM 13
Muscarine, the poisonous component of the death cap mushroom, has the
structure below. We give the proton NMR spectrum. Can you see... |
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347
PROBLEM 14
Treatment with base of the two compounds shown here gives an unknown
compound with the spectra given below. What is its structure?
CHO
+
Cl
O2N
base
?
m/z: 241 (M+, 60%), 90 (100%), 89 (62%)
δH (ppm in CDCl3) 3.89 (1H, d, J 3... |
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Suggested solutions for Chapter 32
PROBLEM 1
Explain how the stereo- and regio-chemistry of these reactions are controlled.
Why is the epoxidation only moderately diastereoselective, and why does the
amine attack where it does?
CO2Me
m-CPBA
CO2Me
O
RNH2
CO2Me
RHN
HO
heat
RN
OH
O
Purpose of the problem
An e... |
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OH
NHR
MeO2C
RHN
OH
O
EtO
RN
OH
O
PROBLEM 2
Explain the stereochemistry of this sequence of reactions, noting the second step
in particular.
N
CO2Et
1. H2, Pd/C
2. NaOEt
3. LiAlH4
N
CO2Et
H
Purpose of the problem
To show how even ‘non-reactions’ can influe... |
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351
PROBLEM 3
Comment on the control over stereochemistry achieved in this sequence.
R1
OH
O
R2
NaBH4
R1
HO
HO
R2
MsCl
Et3N
R1
MsO
MsO
R2
NH3
HN
R2
R1
Purpose of the problem
An exploration of stereochemistry in rings.
Suggested solution
The reduc... |
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Solutions Manual to accompany Organic Chemistry
PROBLEM 4
What controls the stereochemistry of this product? You are advised to draw the
mechanism first and then consider the stereochemistry.
CO2Et
O
1. MeMgBr
2. H
O
O
H
Purpose of the problem
To show how ring-closing reactions, particularly those on the si... |
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353
the ester or acid to allow the lactone to form, but this cyclization gives the cis
lactone directly from the allylic cation intermediate.
Me
O
OR
O
OR
H
O
O
H
H2O
–H
PROBLEM 5
Why is one of these esters more reactive than the other?
H
H
CO2E... |
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Solutions Manual to accompany Organic Chemistry
PROBLEM 6
Explain the stereoselectivity in these reactions.
N
CN
CO2Et
Br
O
N
CN
CO2Et
HO
KOH
N
HO
NH
O
O
1. Cr(VI)
2. NaBH4
N
HO
NH
O
O
K2CO3
Purpose of the problem
Another cyclization reaction and an example of a controlled inversion of
configuration not u... |
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355
N
CN
O
OEt
Br
O
N
CN
CO2Et
O
H
N
CN
O
O
OEt
base
All now depends on the arrangement of the molecule for the cyclization
step. The mechanism is straightforward enough but drawing the transition
state is tricky. We offer two representations: an at... |
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Solutions Manual to accompany Organic Chemistry
Purpose of the problem
Reinforcement of material from chapter 32 and some important reactions.
Suggested solution
Tosylation of the primary alcohol is followed by ester exchange with
methanol to release the anion of a secondary alcohol that promptly closes to
a... |
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357
PROBLEM 8
Draw conformational drawings for these compounds. State in each case why the
substituents have the positions you give. To what extent could you confirm your
predictions experimentally?
OH
H
O
O
HO
Br
Purpose of the problem
Further... |
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marked equatorial Hs in the second compound have each got two axial and
two equatorial neighbours and all the coupling constants will be about the
same and small. They will both appear as narrow triplets of triplets but may
be difficult to analyse. The important ... |
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359
PROBLEM 10
These two sugar analogues are part structures of two compounds used to treat
poultry diseases. Which conformation will they prefer?
O
OMe
Me
HO
O
OH
HO
OMe
Me
Purpose of the problem
Exploration of conformations in natural products ... |
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Suggested solution
The mechanism is formation of a bromonium ion by attack on the electron-
rich alkene, followed by intramolecular nucleophilic attack by the OH group
at the more substituted carbon atom. The NMR spectrum shows that the
protons next to Br and O ... |
http://lib.ysu.am/disciplines_bk/ea4b336028cd91ba7265865d8fde153c.pdf | ea4b336028cd91ba7265865d8fde153c.pdf | true | 519 | Solutions for Chapter 32 – Stereoselectivity in cyclic molecules
361
O
O
RCO3H
O
O
O
F
H
O
O
OH
F
OH
F
O
H
B
OH
F
O
F
O
|
http://lib.ysu.am/disciplines_bk/ea4b336028cd91ba7265865d8fde153c.pdf | ea4b336028cd91ba7265865d8fde153c.pdf | true | 519 | This page intentionally left blank
|
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Suggested solutions for Chapter 33
PROBLEM 1
How would you make each diastereoisomer of this product from the same
alkene?
O
O
Ph
Ph
?
O
O
Ph
Ph
Ph
Ph
?
Purpose of the problem
A gentle introduction to stereochemical control in open-chain compounds.
Suggested solution
The compounds are acetals and can be m... |
http://lib.ysu.am/disciplines_bk/ea4b336028cd91ba7265865d8fde153c.pdf | ea4b336028cd91ba7265865d8fde153c.pdf | true | 519 | 364
Solutions Manual to accompany Organic Chemistry
PROBLEM 2
Explain the stereochemistry shown in this sequence of reactions.
O
R
CO2Bn
Zn(BH4)2
OH
R
CO2Bn
1. O3
2. Me2S
O
OH
R
CO2Bn
Zn(BH4)2
OH
OH
R
CO2Bn
Purpose of the problem
Chelation-controlled reduction is an important method for stereochemical
contr... |
http://lib.ysu.am/disciplines_bk/ea4b336028cd91ba7265865d8fde153c.pdf | ea4b336028cd91ba7265865d8fde153c.pdf | true | 519 | Solutions for Chapter 33 – Diastereoselectivity
365
PROBLEM 3
How is the relative stereochemistry of this product controlled? Why was this
method chosen?
+
I
base
SO2Ph
Li
NH3(l)
OBn
OBn
OBn
SO2Ph
Purpose of the problem
This may seem trivial but the principle is important.
Suggested solution
The relationship ... |
http://lib.ysu.am/disciplines_bk/ea4b336028cd91ba7265865d8fde153c.pdf | ea4b336028cd91ba7265865d8fde153c.pdf | true | 519 | 366
Solutions Manual to accompany Organic Chemistry
Suggested solution
The first LDA molecule removes the OH proton and only the second gives
the lithium enolate. The enolate is held in a ring by chelation to the first
lithium atom so that the allyl group adds to the less hindered face—opposite
the methyl group. ... |
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