Lewis base effects in the Baylis–Hillman reaction of imines with cyclohex-2-en-1-one and cyclopent-2-en-1-one

Abstract

In the Baylis–Hillman reaction of N-benzylidene-4-methylbenzenesulfonamide with cyclohex-2-en-1-one or cyclopent-2-en-1-one, we found that, in the presence of a catalytic amount of DMAP, the Baylis–Hillman reaction can be greatly accelerated to give the normal Baylis–Hillman adduct 1 or 3 in good or very high yields; moreover, using PBu₃ as a Lewis base in the reaction of N-benzylidene-4-methylbenzenesulfonamide with cyclopent-2-en-1-one, the normal Baylis–Hillman adducts 3 could be obtained in very high yields within 5 h, however, using PBu₃ or DBU as a Lewis base in the reaction of N-benzylidene-4-methylbenzenesulfonamide with cyclohex-2-en-1-one, besides the normal Baylis–Hillman adduct 1 abnormal Baylis–Hillman adduct 3-aryl-2-[(4-methylphenyl)sulfonyl]-2-azabicyclo[2.2.2]octan-5-one 2 was formed at the same time; the substituent’s effects were also examined.