CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

acetophenone (59l) under a solvent-free condition was largely unsuccessful, 87a although the
In-mediated allylation of 59l and 59q was reported in water. 65b
So far, Ga-mediated
allylation of only one ketone, 59l has been reported. 87b Thus, this protocol was more
versatile and could be used even for the bulky and electronically demanding substrates
such as 59m-59p. As in earlier cases with In mediated allylations, the formation of
homoallylic alcohols was confirmed from the hydroxyl band at ~3500 cm -1 along with the
terminal olefinic band at 910-930 cm -1 in the respective IR spectrum. Furthermore, all the
products showed 1 H NMR resonances at δ 5.0-5.2 (2H) and δ 5.7-5.9 (1H), and 13 C NMR
resonances at δ ~114 and δ ~134 due to terminal olefins. As representative examples, the
1 H NMR and 13 C NMR of 60g are shown in Fig. II.3.7 and Fig. II.3.8.
Chemo- and stereoselective allylation of multifunctional compounds is one of the
most fundamental goals in constructing complex molecules. The new protocol of allylation
proceeded with complete chemoselectivity with the conjugated carbonyls, 59g and 59o,
furnishing the respective 1,2-addition products 60g and 60o only, while only the mono
allylated product 60n was obtained with the diketone 59n. Interestingly, allylation of 2-
methylcyclohexanone (59q) under the above conditions exclusively furnished E-60q in
excellent yield (Table II.3.4, entry 16).
Table II.3.4. Reaction profile of Ga-mediated allylation of various aldehydes in
[bmim][Br] a
Entry Substrate R 1 R 2 Product Time (h) Yield
(%) b
1 59b 4-Br-C 6 H 4 H 60b 6 77
2 59c 3-OMe-C 6 H 4 H 60c 5 84
57