Synthesis of Spiro-fused Nitrogen Heterocyclic Compounds via N-Methoxy-N-acylnitrenium Ions Using Phenyliodine(III) Bis(trifluoroacetate) in Trifluoroethanol

Abstract

Spirodienones and spirodienes bearing the nitrogen atom bound to the spiro carbon have been synthesized from N-methoxy-(4-methoxyphenyl)amides and N-methoxyphenylamides, respectively, by the intramolecular ipso attack of a nitrenium ion generated with phenyliodine(III) bis(trifluoroacetate) in trifluoroethanol.Transformation of benzenoid compounds to nonbenzenoid compounds can provide valuable intermediates for the synthesis of a variety of organic compounds. 1 In previous work, we reported the synthesis of spirodienones bearing the nitrogen atom bound to the spiro carbon atom.The procedure involved intramolecular ipso attack of a nitrenium ion generated from an N-chloro-N-methoxyamide moiety appended to the oor p-methoxybenzene substrate. 2Very recently the same type of the ipso cyclization has been performed to afford spirodienone compounds using phenyliodine(III) bis(trifluoroacetate) (PIFA). 3ese spiro compounds have proved to be valuable intermediates for the synthesis of biologically important compounds. 4 now report the successful development of a useful new method for the selective conversion of benzenoid compounds, such as N-methoxy-(4-methoxyphenyl)amides (1a-c) and N-methoxyphenylamides (3a-i), to 2,5-cyclohexadienone (2a-c) and 2,5-cyclohexadiene derivatives (5a-i and 6), respectively.This new procedure features intramolecular ipso attack of a nitrenium ion generated with PIFA under mild reaction conditions.We have initiated efforts to undertake the synthesis of spirodienones using PIFA instead of t-BuOCl, since the latter presents environmental problems related to disposal.