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HOW TO APPROACH EXAMINATION QUESTIONS: SELECTED PROBLEMS AND ANSWERS
(c) Draw taxol in the form of a Newman projection looking down the 2–3 bond, and showing the stereochemically
preferred conformation.
(d) Draw the enantiomer of taxol, using wedge–dot convention.
(e) Give a mechanism for the reaction of taxol with acetic anhydride [(CH 3 CO) 2 O].
(f) What products would be produced if taxol were treated with hot, aqueous HCl?
Answer 16.01
This is a relatively complex molecule, but these are simple questions requiring only standard procedures and
reasoning.
(a) Ester, amide.
OR
O
OH
NH
O
1
2
3
Ph
Ph
ester
amide
(b) 2R, 3S.
chiral centres have four different groups attached
priority 1
priority 2
priority 3
OR
O
OH
NH
O
2
Ph
Ph
OR
O
OH
NH
O
3
Ph
Ph
H
H
H
don't put in the wedged
hydrogen like this: it is
more difficult to visualize
the stereochemistry
priority 1
priority 2
priority 3
the sequence 1 → 2 → 3 looks anticlockwise
from front, but must be viewed from the rear
towards H; therefore it is clockwise: (R)
the sequence 1 → 2 → 3 looks clockwise
from front, but must be anticlockwise
looking from the rear towards H: (S)
O
C
O
O
N
C
C
C
C
C
C
C
C
O
priority 4
priority 4
carbon-2
carbon-3
(c)
OR
O
OH
H
N
O
Ph
Ph
2
3
view from
this side
CO 2 R
OH
H
Ph
NHCOPh
H
OH
H
RO 2 C
Ph
NHCOPh
H
rotate front groups; minimum
interaction of large groups
corresponds to when H atoms are anti
rotate front
group 120˚
3 interactions
2 interactions
H
H