Selenium Dioxide Oxidations in the b-Carboline Area

Abstract

The reaction of 1-ethyl-3-methoxycarbonyl-l, 2,3,4-tetrahydro-0-carboline 11 with selenium dioxide has re--sulted in the synthesis of the 0-carboline alkaloids, l-acetyl-3-methoxycarbonyl-6-carboline 14 and 1-acetyl-0-carboline 15.-" --Application of this technology in a different series has resulted in a two step synthesis of canthin-6-one.The scope and/or limitations of the reaction of tetrahydro-0-carbolines with selenium dioxide are discussed.Although there are relatively few methods available for the preparation of 3-acylindoles, most notable for the present discussion are the thioketal approach of ~tad1er.l the DDQ method developed by yonemitsu2 and the work with selenium d i ~x i d e , ~ the recent isolation of several natural products which contain the 3-acylindole moiety has stimulated additional interest in this area.Alkaloids of particular importance are borrecapine l r 4 aristotelinone 2 , 5 crenatine 3 , 6 1-methoxy-canthin-6-one7 and pimprinine.8The latter base was synthesized by ~oshi,' and more recently by Yonenitsu (DDC technology!. 10Recently we have shown3 that the indole piperido base 4 could be converted the 3-acylinllole 5 or to the 3-acylpyridoindole 6 in good to excellent yields