Dimethyl sulfide–boron trihalide-mediated reactions of α,β-unsaturated ketones with aldehydes: one-pot synthesis of Baylis–Hillman adducts and α-halomethyl enones

The reactions of aldehydes with 3-buten-2-one (2) were conducted in the presence of BBr3·Me2S or BCl3·Me2S and then worked up with aqueous NaHCO3, affording the α-methylene aldol 3, α-halomethyl aldol 4 or 6, and α-halomethyl enones 5 or 7, respectively. In contrast, the reactions quenched with water gave the α-halomethyl enones 5 or 7 in high yields, while the work-up with an aqueous 10% trimethylamine gave the α-methylene aldol 3. The phenol 15 and half-acetal 16 were obtained from the reaction of p-nitrobenzaldehyde (1a) with cyclohexenone (10).