摘要:
[GRAPHICS]Treatment of alpha -alkylidenelactones 3a-d with Bu3SnH and a catalytic amount of Et3B effected a 5-exo radical cyclization preferentially to provide the corresponding 1 and 2 in a ratio of 70:30 to 100:0, Meanwhile, the reaction of 3a and 3b in the presence of Et2AlCl proceeded via a B-endo cyclization pathway predominantly to afford 2a and 2b with 90% and 92% regioselectivity, respectively.