An efficient synthesis of 1,3-dimethyl-4-(phenylsulfonyl)-4H-furo3,4-bindole

摘要

The fused heterocyclic ring system 4H-furo3,4-bindole (1) has served admirably over the past 20 years as a stable indole-2,3-quinodimethane (2) synthetic analogue in Diels-Alder reactions.~1,2 We have utilized this ring system in syntheses of isomeric benzocarbazoles,~1a,b,b,f bis(benzobcarbazoles),~1c and pyridocarbazoles includig the antiumor alkaloid ellipticine (3).~1d,e,2h Our synthesis of ellipticine successfully employed the 1,3-dimethyl analogue 1 (R=Me). Unfortunately, our two original methods for the syntheses of 1 (R=Me) were lengthy. We now describe a very convenient and efficient synthesis of 1,3-dimethyl-4-(phenylsulfonyl)-4H-fouro3,4-bindole (1 R=Me). Our new method has the advantage over the earlier methods in that oxidation and reduction steps are avoided in the manipulation and formation of the furan ring.