CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

IV.1.3: Present work
Although several syntheses of compound V exist, most of these need multiple steps
and expensive reagents. This prompted us to formulate an efficient and operationally
simple synthesis.
From retrosynthetic analysis (Scheme IV.1.4), we envisaged that easily accessible
(R)-2,3-cyclohexylideneglyceraldehyde 1 could be used as a suitable chiral template for the
construction of its C-2-alkylated stereogenic moiety via allylation with the allylic bromide
78 described in Chapter III.1.2. Based on the synthetic plan, the diastereomers 79a and
79b possesses the stereochemistry at the alkyl branched centre as is present in the target
compound. The protected triol moiety of 79a/79b can be converted to the propyl group as
in a1. Oxidative cleavage of the alkene functionality in a1 would furnish the required
carboxylic acid group.
COOH
C 6 H 13 C 6 H 13
HO
OH
OH
V a1 a2
C 6 H 13
O
O
C 6 H 13
OH
79a/79b
O
O
1
CHO
Scheme IV.1.4
Earlier (Chapter III.1.2), using bimetallic redox strategy, the diastereomers (79ac)
were synthesized by allylation of 1 with the bromide 78. Using the bimetallic redox
strategy involving a combination of CuCl 2 .2H 2 O and Zn, the reaction of 1 with (Z)-78b
yielded 79b as the major diastereomer (shown in previous chapter). This was used for the
present synthesis. For the required deoxygenationof its 1,2,3-triol unit to the C 3 H 7 -
moietycompound 79b was tosylated to afford 105. This was characterized from the
142