NEW EFFECTIVE CATALYSTS FOR MUKAIYAMA-ALDOL AND MUKAIYAMA-MICHAEL REACTIONS - BICL3-METALLIC IODIDE SYSTEMS

Metallic iodide-activated bismuth(III) chloride efficiently catalyzes the Mukaiyama-Aldol and -Michael reactions. Some examples of reactions of silyl enol ethers derived from acetophenone and cyclohexanone (I and 2, respectively) with aldehydes, ketones, acetals, and alpha-enones are given. The cross-over aldolization between 1 and benzaldehyde in the presence of BiCl3-l.5ZnI2 or BiCl3-1.5SnI2 systems (5 % mol) has been carried out quantitatively at -30 and -78-degrees-C, respectively. For this reaction a similar activation has been also observed with antimony(III) chloride. X-ray patterns of catalytic systems show the formation of bismuth(III) iodide by CI/I-exchange reaction between BiCl3 and metallic iodide (NaI, ZnI2, SnI2,...). These results.have been rationalized with a two-step mechanism in which a key feature seems to be the activating role played by BiI3 toward the cleavage of the Bi-chelate intermediate by the chlorosilane formed. Ultrasound activates significantly the catalytic power of these metallic halide systems.