CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

in [bmim][BF 4 ] using sub-stoichiometric amount of Sn. Such a protocol with In metal in
RTIL is unprecedented.
Subsequently, the catalytic protocol (0.2 equiv. of In) was extended to the other
aromatic and aliphatic aldehydes 59b-j (Table II.3.2, entries 4-12). The protocol was
equally effective with both aromatic and aliphatic aldehydes, furnishing the products 60b-j
in good yields. The nature of the substituents in the aromatic ring or alkyl chain length did
not have any appreciable effect on the course of the reaction. The slow reaction of 59h was
surprising. With the conjugated aldehyde 59g, the reaction proceeded with complete
chemoselectivity furnishing the 1,2-addition product 60g only. The products, obtained
from the allylation reaction in [bmim][Br] could be conveniently isolated by extracting the
reaction mixture with Et 2 O followed by concentration. The reactions were clean without
any side products and/ or starting materials. The RTIL was reused three times after
discarding the metallic products, settled at the bottom of the flask.
Overall, the above results clearly established [bmim][Br] as the best RTIL among
those chosen for the In-mediated allylation. Under stoichiomteric conditions, the reactions
proceeded much faster in [bmim][Br] without needing any metal activator, and furnished
the products in excellent yields in only 4-5 h. Most importantly, the reaction could be
carried out using only 0.2 equiv. of the metal. In contrast, even with stoichiometric
amounts of In, it required overnight stirring in the other RTILs, while a large excess of the
reagents and extended time were essential for the reaction in H 2 O and THF. The marked
metal activation provided by [bmim][Br] as well as the requirement of only catalytic
amount of In were of interest for further studies.
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