Download Answer Key to Assignment #7

Chem 2600
Assignment 7 Answer Key
1. a) Predict the major product for each of the following reactions:
Br
+ HBr
+ HBr
Br
ROOR
(Peroxide)
b) Rationalize the observed regiochemistry, where appropriate, for each of the preceding reactions. If your
answer involves a key intermediate, give its structure.
The top reaction proceeds through a cation intermediate. The most stable available carbocation gives rise to the
observed Markovnikov product.
The bottom reaction proceeds through a free radical mechanism, so a different intermediate leads to the observed
product.
Br
Br
2. How would you prepare the following molecules? More than one step may be necessary. You may use any
reagents/solvents you wish.
Br
Br2
(H3C)3C
O
K
E2
Br
Br
OCH3
CH3 OH
SN1
Br2
Br
Br
OH
SOBr2
Convert OH to leaving
group - either halide or
sulfonate
Br
E2 (t-Butoxide)
H+, H2O
O
Oxidize, PCC, PDC,
Jones, or Swern
CH3
OH
3. Predict the organic product(s) of the following reactions. If more than one organic product is formed, show
them all and indicate, if possible, which is/are the major products. Be careful to clearly indicate the relevant
stereochemical results (using dashed and wedge bonds where appropriate). If a racemic mixture results, a
statement to that effect will suffice.
i) The products are both racemic.
O
H
O2N
CO 2 Et
CO 2 Et Et O 2 C
O
O2N
O
H
ii)
1)
O
B H
O
Ph
Ph
Ph
Ph
2 ) C H 3 CO 2 H
iii)
H
H
H
H 2 , Pd / C
H
iv)
1) BH 3 , T HF
2) H2 O 2 , N a O H
H
OH
NO2
Ra c e m ic
4. Develop syntheses of the following compounds using 1-methylcyclopentene.
O3, H 2O2
HO
O
O
C
C
O3, S(CH3)2
H
5.
1) NaCN
CH3
O
O
C
C
Target
2) H+
CH3 OH, H+
Target
CH 3
i) Both hydrogens of acetylene can be removed by reaction with n-butyllithium to give dilithium acetylide
– an ambident nucleophile. With this in mind, show how you would make the following molecule from
acetylene and benzaldehyde.
H
H
n-BuLi
Li
Li
2 PhCHO HO
OH
Ph
Ph
H2 , Pd/C
OH HO
Ph
Ph
ii) Comment on the stereochemical outcome of this reaction.
The product has two new chiral centers. You will get three stereoisomeric products: a meso compound
(RS) and a racemic mixture of RR and SS products.
6. Describe how you would carry out the following transformations. More than one step may be necessary.
The aldehyde must be protected first,
O
O
O
H
H
OCH3
CH3 OH, H+
OCH 3 O
H3CO
H+, H2O
LAH, ether
H
OH
OCH3
H3CO
OCH3
H
OH
7. What would be the products of ozonolysis of the following alkenes followed by reductive workup?
O
O
OH
O
ox
HO
r ed
O
HO
O
O
ox
H
O
OH
O
r ed
O
O
H
Bu
OH
O
Bu
ox
r ed
O
HO
H
Ph
H
Ph
Bu
H
O
O
H
Ph
H
OH
ox
O
+ HCO2 H
r ed
O
+ CH2 O
8. How might you distinguish between the following two isomeric alkenes using a chemical test?
Ozonolysis of the first will give a single product, propanal (via the reductive workup). The second will give a
mixture of two products, butanal and acetaldehyde.
9. How would you prepare the following compound using a Diels-Alder reaction followed by reductive
ozonolysis? Note the stereochemistry.
O
O
H
H
H 3 CO 2 C
H 3 CO 2 C
H 3 CO 2 C
Diels-Alder reaction of cyclopentadiene and methyl acrylate gives the endo adduct shown. Reductive ozonolysis
gives the final product. Note that the stereochemistry of the Diels-Alder reaction has allowed you to fix the
relative stereochemistry (not absolute stereochemistry) of three chiral centers.
10. Suggest syntheses of the following alcohols, all of which can be derived from methylcyclopentene. The
number of arrows indicate the number of reactions that are needed.
1 ) KMn O4 or O s O4
CH 3
OH
HO H
CH 3
OH
2 ) Pe r a cid t o for m t h e ep oxid e ,
CH 3 fo llo w ed b y e p o xi d e o p e n in g w ith
H
Na O H o r a q . H 2 SO4
2
3
1
H OH
4
H OH
5
CH 3
H
CH 3
OH
HH
HO H
3 ) Hy d r o b or a t io n follo w ed b y
r ea c t ion wit h ba sic H2 O 2
4 ) Co n ve r s ion of t h e h y d r oxy l
gr ou p in t o a s u lfo n a t e es t e r l ea v in g
gr ou p . (CH3 SO 2 Cl, p y rid in e ) Th en
SN 2 r e a ct io n w it h h y d r oxid e . Migh t
give a lo t o f E2 , t h o u gh .
5 ) Aq . H 2 SO4