LEWIS ACID-PROMOTED REACTIONS OF 3-METHOXY-N-(BENZENESULFONYL)-1,4-BENZOQUINONE MONOIMINE WITH PROPENYLBENZENES

BF3 . OEt2-promoted reactions of 4-N-(benzenesulfonyl)-3-methoxy-1,4-b enzoquinone monoimine (5) with (E)-propenylbenzenes bearing strong ele ctron-donating groups on their aromaric rings produce -methoxy-3-methy l-5-[N-(benzenesulfonyl)amino]-2,3 -diydrobenzofurans (6). With neutra l propenylbenzenes, either the dihydrobenzofurans, bicyclo[3.2.1]octen ediones 17, or products of tandem cycloaddition (7-9) are formed depen ding upon reaction conditions. In the latter, molecules with seven to eight asymmetric centers are formed in a single reaction from achiral starting materials. Thus, these seemingly simple reactions yield produ cts of remarkable complexity, and with a high degree of stereoselectiv ity.