Oxidation of Cycloalkan[b]indoles with Iodine Pentoxide (I2Os)

Abstract

Oxidation of cycloalkan[b]indoles (3) with iodine pentoxide (I205) in 80% aqueous tetra-hydrofuran (THF) at room temperature regioselectively afforded 6-oxocycloalkan[b]indoles (4) in various yields. The yield of this oxidation depends on the size of the ring fused with the indole nucleus. The essential reaction species is I2Os, not HI03, which might be generated by hydrolysis of I2Osin the aqueous reaction medium. Oxidation of 1-hydroxytetrahydrocarbazole (5) under the above conditions afforded spiro oxindoles 6 and 7 in 36 and 39% yields, respectively, accompanied with only a trace of 1-oxotetrahydrocarbazole (4a). © 1987, The Pharmaceutical Society of Japan. All rights reserved.