CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

species is a prerequisite for any metal mediated addition of organic halides to carbonyls,
both under anhydrous and aqueous conditions. Hence, the metal activation, either as a
whole or at its surface that enables the metal to insert into the C-halogen bond of the
organic halides, has become an important technique for preparative organic chemistry. For
surface activation of the metals, several techniques viz. addition of I 2 or CH 2 I 2 to Mg for
the preparation of the Grignard reagent, sonication of metals (Mg, Zn, Sn, Cu etc), 60d
treatment of Zn with aqueous NH 4 Cl for allylation 3,60 and BF 3 -ethereate for Reformatsky
reactions, 105 cementation 106 to form a surface alloy etc. are employed. Rieke et al. 107 have
introduced a general approach for the preparation of several active metals employing the
reduction of the corresponding metal halides with K, Li etc. The simultaneous co-reduction
of two metal salts by complex hydrides 108 (e. g. NaBEt 3 H), potassium graphaite, 109 or
electrolysis 110 have also been utilized for the generation of highly active bimetallic systems
such as bimetallic colloids, alloys, and intimate conglomerates of very fine metal particles.
However, most of these strategies operate strictly under anhydrous conditions.
IIIIII. .11. .22 PPrreesseennt t Woorrkk
The lack of metal activation procedures in aqueous medium led us to formulate a
bimetallic redeox strategy in which a metal salt is used in combination with a reducing
metal. The metal salt, after reduction, produces the highly active metal. This, in turn, reacts
with the allylic/benzylic halides to form the active organometallic species. This strategy
works well even in moist condition. For, this, several combinations of metal halides viz.
CuCl 2. 2H 2 O, CoCl 2. 6H 2 O, FeCl 3 and SnCl 2 .2H 2 O and reducing metals such as Zn and Mg
were used to generate the active metals. The chiral aldehyde (R)-2,3-
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