CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

(OH). Oxidative cleavage of its α-glycol with NaIO 4 furnished the aldehyde 141. It was
characterized from the IR peaks at 1730 and 1712 cm -1 , as well as 1 H and 13 C NMR peaks
at δ 9.35 ppm and δ 203.4 ppm respectively for the –CHO group. Reaction of 141 with
PhMgBr proceeded with excellent diastereoselectivity (dr >98:2) to furnish the target
cryptophycin unit-A equivalent 142 as the major product. Formation of 142 was confirmed
from the appearance of IR peak at 3478 cm -1 and the 1 H NMR resonances at δ 4.88-4.97
(m, 2H) which accouted for both PhCH(OH) and -CH(OBz) protons. For further
confirmation of its structure, compound 142 was converted to the known compound 144,
that has been conceived as an advanced synthon for cryptophycin A. 155b Thus, compound
142 was desilylated and the resultant product converted to the acetal 143 by an acid
catalyzed condensation with DMP. Formation of 143 was confirmed from the
disappearance of the hydroxyl peak in its IR spectrum, as well as appearance of two
singlets at δ 1.58 and 1.62 ppm in the 1 H NMR spectrum. Its subsequent debenzoylation
finally afforded the target synthon 144, whose spectral and optical data were in accordance
with those reported. 155b
156