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-benzoquinone monoimine (5) with (E)-propenylbenzenes bearing strong electron-donating groups on their aromaric rings produce 2-aryl-6-methoxy-3-methyl-5-[N-(benzenesulfonyl)amino]-2,3 -diydrobenzofurans (6). With neutral propenylbenzenes, either the dihydrobenzofurans, bicyclo[3.2.1]octenediones 17, or products of tandem cycloaddition (7-9) are formed depending 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 products of remarkable complexity, and with a high degree of stereoselectivity.