A New Method for the Construction of Indole Nucleus

Directed lithiation of N-rerr-butoxycarbonylanilines and subsequent reaction with I-ferr-buryldimethylsilyl-I-phenylsulfmylethene gave the conjugate addition products which, without isolation, were cyclized to l-rertbutoxycarbonyl-2-phenylthioindolines under thermal sila-Pummerer reaction conditions.Since the fust synthesis of indole by von Baeyer in 1866,' a number of the synthetic methods for this heterocyclic system have been devised mainly due to significant biological activities of the indole natural products.2Although a variety of well-established classical indole syntheses are available,-) the newer syntheses, which focused on the regioselective construction of highly functionalized indoles, have been still actively investigated.4In this communication, we wish to repon a new synthesis of the indole ring system based on the consecutive directed lithiation-conjugate addition-sila-Pummerer rearrangement strategy.The directed orrho-lithiation of N-terr-butoxycarbonylaniline ( l a ) has been reported by ~u c h o w s k i and Venuti.5The generality of this reaction has been demonsuated in the lithiation of a range of N-!errbutoxycarbonylanilines.6 On the other hand, the conjugate addition of organolithium and Grignard reagents to 1-trimethylsilyl-1-phenylsulfinylethene (Za) has been reported by Kanemasa, ef al.7 By a combination of these two reactions, we obtained a following idea for the preparation of indole ring system (Scheme 1).