Mn(III)-BASED OXIDATIVE CYCLIZATION OF N-ARYL-3-OXOBUTANAMIDES. FACILE SYNTHESIS AND TRANSFORMATION OF SUBSTITUTED OXINDOLES (Dedicated to Professor Isao Kuwajima on the occasion of his 77th birthday)

The oxidation of 3-oxo-N-phenylbutanamides 1 with manganese(III) acetate in ethanol afforded dimeric 3,3'-biindoline-2,2'-dione derivatives 3–5. A similar reaction of N,2-disubstituted N-aryl-3-oxobutanamides 6 in acetic acid produced 3-acetylindolin-2-ones 7 bearing various substituents in good to excellent yields. The acetylindolinones 7 were easily deacetylated by treatment using neutral alumina in diethyl ether. Both the acetylindolinones 7 and deacetylated indolinones 8 were transformed by reduction into the substituted 1H-indoles. INTRODUCTION Many of the chemistries for indoles and their derivatives have been investigated and reported. However, the synthesis and reaction of these heterocycles are still attractive from the view point of the synthetic method, total synthesis of natural products, biological and pharmacological activities, and material science. Recently, we reported the Mn(III)-mediated direct substitution of methoxynaphthalenes with N-aryl-3-oxobutanamides, giving the 3-oxobutanamide-substituted naphthalene I in addition to a small amount of demethoxylated naphthofuran II and benzoindolinone III (Scheme 1, eq. 1). Although the yield of the heterocyclic compounds II and III was poor, the carbon-carbon bond formation efficiently occurred during the reaction. We also reported the facile synthesis of 3,4-dihydro-2(1H)-quinolinones, 540 HETEROCYCLES, Vol. 90, No. 1, 2015