CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

O
O
O
iii iv
O
132a
+
O
O
i,ii
OR 1 O
131 R 1 = TBDPS
133 R 1 = Bz
OBz OH
134
OH
135
OH
(i) Bu 4 NF, THF, 0 o C; (ii) BzCN, Et 3 N, 25 o C; (iii) NaBH 4 , MeOH, 0 o C; (iv) K 2 CO 3 ,
MeOH, 25 o C.
Scheme IV.2.5
For the actual synthesis of the target compound (Scheme IV.2.6), the carbinol 132
was benzoylated to furnish the compound 136, which was characterized from the IR peak
at 1638 cm -1 , and the 1 H NMR multiplets at δ 5.45-5.52 for the –CH(OBz) group.
Desilylation of 136 gave the alcohol 137, which showed IR hydroxyl band at 3437 cm -1 ,
and absence of characteristic 1 H NMR resonances for the TBDPS group. Oxidation of the
carbinol function of 137 with PCC followed by reduction with K-selectride ® gave the 1,3-
anti diol derivative 138. As done for compound 132, the relative 3,5-anti stereochemistry
of 138 was ascertained by converting it (Scheme IV.2.6) to the cyclic acetal 138b through
the diol 138a, followed by 13 C NMR analysis. 156 Appearance of the peak at δ 23.9, 24.0
and 100.3 ppm in the 13 C NMR spectrum confirmed its anti-stereochemistry. Next, the
alcohol 138 was silylated with TBDPSCl and imidazole to get compound 139, which was
characterized from the appearance of 1 H and 13 C peaks due to –TBDPS group.
Deketalization of 139 with aqueous TFA, gave the diol 140 uneventfully. The 1 H NMR
(Fig. IV.2.6) and 13 C NMR (Fig. IV.2.7) spectra of 140 showed the absence of resonances
due to cyclohexylidene moiety, while its IR spectrum revealed a broad peak at 3438 cm -1
155