Level 2 – Case 28
184
E Ex xp pe er ri im me en nt ta al l D Da at ta a
1. Lithiation of N-benzoyl oxazolidine
N N
4 with either t-BuLi or s-BuLi in the presence of DMPU, at –78°C, followed by quenching with an electrophile, yielded
tricyclic products 5 as single diastereomers.
1 On stirring 5 with acid (2M HCl in
ether) a clean epimerization takes place to yield compounds 6 (Scheme 28.2).
N
O
O
N
N O
2) E +
N
O
E
H H
2M HCl
O
N
E
H H
5
4
6
1) s-BuLi
DMPU
E = H, D, Me, Bn
O
O
Scheme 28.2
2. Lithiation of 4 in absence of DMPU, followed by rapid quenching (after 30
min) at –78°C with CD 3 OD only yielded ortho-deuterated product 7 (95%). By
repeating this sequence, both ortho protons could be replaced by deuterium to
give 8 (Scheme 28.3).
N
O
O
3 OD
N
O
O
D
2) CD 3 OD
N
O
O
D
D
4
1) s-BuLi
7
1) s-BuLi
8
Scheme 28.3
3. Treatment of naphthamide 9 with t-BuLi at –78°C for a period of 2 h, followed
by electrophilic quenching with D 2 O led to a 1:2 mixture of products 10 and 11
(Scheme 28.4).
1 The evidence of the stereochemistry of compounds 5 was gained from X-ray crystallography and nuclear Overhauser effect (NOE) studies.