CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

possible diastereomers 83a-d in substantial amounts, using two operationally simple
protocols.
O
O
R
i
O
O
R
ii
83b
R = CH 2 OTBDPS
83c
OH
O
84c
O
O
R
i
O
O
R
ii
83a
83d
OH
O
84d
83d
iii
O
O
85
R 1
OBz
iv
v
RO
OH
R 1
OBz
86 R = H
87 R = TBDPS
vi
TBDPS O
O O
BzO CH 2 OTBDPS
88
(i) PCC, NaOAc, CH 2 Cl 2 , 25 o C; (ii) K-selectride ® , THF, -78 o C; (iii) BzCl, pyridine,
CH 2 Cl 2 , 0 o C; (iv) Aqueous CF 3 CO 2 H, CH 2 Cl 2 , 0 o C; (v) TBDPSCl, imidazole, CH 2 Cl 2 , 25
o C; (vi) O 3 , NaOH in MeOH, -15 o C.
Scheme III.1.8
Next, using the alcohol 83d as the model substrate, the relative 3,4-stereochemistry
was determined. For this, it was converted to the corresponding benzoate derivative 85 in
95% yield, by treating with BzCN in the presence of pyridine. The absence of any IR
hydroxyl band, and presence of 1 H NMR multiplets at δ 5.66-5.71 (1H) (Fig. III.1.16) and
13 C NMR peak at δ 165.5 (Fig. III.1.17) confirmed its formation. Compound 85 was
subjected to deketalization with aqueous TFA in CH 2 Cl 2 to afford the diol 86 in 86% yield.
The broad IR band at 3411 cm -1 was indicative of the diol function. This was confirmed
from the absence of 1 H NMR and 13 C NMR resonances (Fig. III.1.18 and Fig. III.1.19
100