CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

thermogavimetric and elemental analyses. The intermediate IIIa subsequently reacted
with allyl bromide to furnish the active allylating species III (characterized by 1 H NMR
spectrum and synthesizing it separately), and generating active Ga-metal surface for
sustaining the reaction. The entire mechanistic pathway is presented in Scheme 3.
Chapter III: Diastereoselective synthesis of chiral carbinols
Given that the major interest of the study was the development of some
asymmetric protocol for allylation, two substrate-controlled approaches were explored for
this purpose, using (R)-cyclohexylideneglyceraldehyde 3 7 as the chiral template. In one of
these, a bimetallic redox strategy was employed for allylation and even for benzylation. In
the other approach, different metal-solvent combinations were used to tune the
diastereoselectivity of the Barbier type allylation. For both these, unsubstituted and γ-
alkylated allyl bromides were used. The results of the studies are presented below.
The bimetallic redox strategy involves spontaneous reduction of a metal salt
(M 1 X) in aqueous environment with another metal (M 2 ) that have higher oxidation
potential, to produce the activated metal (M 1 ). This, in turn, reacts with allylic bromides
to give the active allyl-metal species, which eventually reacts with the aldehyde 3. Based
on its higher oxidation potential compared to Fe, Co, Cu and Sn, Zn was chosen as the
reducing metal in separate combinations with the commercially available salts viz.
Zn/CuCl 2. 2H 2 O, Zn/CoCl 2. 6H 2 O, Zn/FeCl 3 and Zn/SnCl 2 .
Different allylic bromides viz. 1-bromo-4-hydroxy-cis-2-butene (4), 1-bromo-2-
butene (6) and 1-bromo-2-nonene (8) were reacted with 3 in the presence of the above
viii