Padwa et al.: A Novel Oxidative Rearrangement of N-Furanyl Carbamates... Scientific paper A Novel Oxidative Rearrangement of N-Furanyl Carbamates Uncovered During a Planned Synthesis of a Daphniphyllum Alkaloid

E-Dimethyl 2-(2-oxycyclopentylidene)succinate was prepared by the TiCl4 catalyzed [2+2]-cycloaddition of (trimethyl-silyloxy)cyclopentene with DMAD followed by a base induced ring opening of the initially formed cycloadduct. It was necessary to protect the keto group as the 1,3-dithiane in order to prepare the corresponding N-furanyl carbamate 16. Loss of the Boc group occurs on heating at 130 °C or upon treatment of 16 with Mg(ClO4)2. In an attempt to convert the 1,3-dithiane of the resulting NH-carbamate 17 to the corresponding carbonyl group, the compound was treated with io-dine in a basic aqueous solution. Under these conditions, a rather unusual oxidative rearrangement occurred to produce a substituted 5-hydroxy-1H-pyrrol-2(5H)-one. Analogous oxidative rearrangements were found to occur with structu-rally related 2-amidofurans. The mechanism of the oxidative rearrangement is comparable to the aza-Achmatowicz reaction