CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

4 1d 4-(CH 3 ) 2 CH-C 6 H 4 1 : 1.5 : 0.2 22 2d (91)
5 1e 4-C 6 H 5 - C 6 H 4 1 : 1.5 : 0.2 20 2e (86)
6 1f C 6 F 5 1 : 1.5 : 0.2 18 2f (88)
7 1g C 6 H 5 CH=CH 1 : 1.5 : 0.2 22 2g (86)
8 1h (CH 3 ) 2 CH 1 : 1.5 : 0.2 48 2h (68)
9 1i CH 3 (CH 2 ) 5 1 : 1.5 : 0.2 22 2i (87)
10 1j CH 3 (CH 2 ) 8 1 : 1.5 : 0.2 22 2j (91)
a The reactions were carried out at 2 mmol scale using 20 mol% In. The yields refer to
those of isolated pure products.
Regarding the catalytic role of In metal in the reaction, its oxidation by
[bmim][Br] generated InBr 3 , which eventually produced In +1 (InBr) at the acidic pH (5.78)
of [bmim][Br] following the equilibrium 2 In (s) + In +3 = 3 In +1 . The species II was
produced by the reaction of allyl bromide with InBr, as well as the activated In metal.
Finally reaction of II with the aldehyde followed by hydrolysis of the intermediate with
the trace amount of H 2 O (present in [bmim][Br]) furnished the allyl alcohol. The InBr 3 ,
generated in the process got reduced by the [bmim] radicals to form [InBr 2 ] radical or its
dimer, which finally disproportionated to give InBr, thus maintaining the cycle without
further addition of In metal.
The Ga-mediated allylation of the aldehydes 1a-k, and even ketones 1l-q (Scheme
2) also followed a similar course to furnish the respective homoallylic alcohols (Table 2).
The protocol proceeded with complete regio- (mono allylated product with the diketone
1n), chemo- (1,2-addition with the conjugated carbonyls 1g and 1o, and diastereoselectivities
(exclusive formation of trans-product with 1q).
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