HETERO-DIELS-ALDER VS MUKAIYAMA ALDOL PATHWAYS IN THE REACTION OF MONOACTIVATED DIENES AND ALDEHYDES - A LEWIS-ACID STUDY

The effect of Lewis acid on the reaction of 2-monoactivated dienes and aldehydes was studied searching for more general reaction conditions than those previously published. It was found that BF3-OEt(2) in dieth yl ether gave the best yields of Diels-Alder adducts with good endo/ex o selectivities. The Mukaiyama aldol-Michael cyclization pathway which has been reported to occur with this Lewis acid in the reaction of di activated dienes, does not seem to operate with the monoactivated ones . Other Lewis acids gave good yields of silylated aldol products, and a crossover experiment showed that the recently proposed silatropic-en e pathway does not occur under the conditions used.