Rhodium-Catalyzed Reactions of a Vinyldiazoacetate with N-Substituted Semicyclic Enaminones

Andreas Müller, Andreas Endres and Gerhard Maas*

Institute for Organic Chemistry I, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany

* Corresponding author: E-mail: gerhard.maas@uni-ulm.de

The rhodium-catalyzed reaction of dimethyl 3-diazo-1-propene-1,3-dicarboxylate (4) with N-substituted five-membered semicyclic enaminones 1 yields (3-ammoniopropyl)cyclopentadienides 7 and/or dienamines 8 which formally represent products of carbenoid insertion into the enaminic β-C–H bond of 1. The thermal isomerization 87 is facilitated by electron-donating substitutents at the N atom and at the carbonyl group of the enaminone moiety. Thus, N-alkyl substituted dienamines 8 in general undergo the isomerization, while N-phenyl substituted analogues do not rearrange. The isomerization behavior of the N-methyl-3-(anthracen-9-ylcarbonyl)-substituted dienamine 8c is complex: isomerization into betaine 7c is achieved in low yield in the presence of sodium methanolate, while thermal impact in the presence of silica gel generates pentacycle 9 as a result of an intramolecular Diels-Alder reaction at the anthracene moiety. In complete analogy to the transformation 18, the rhodium-catalyzed reaction of vinyldiazoacetate 4 with the dimedone-derived 3-morpholinocyclohex-2-en-1-one 11 yields the olefinic C–H insertion product 12.

Keywords: Cyclopentadienides, diazo compounds, dienamines, enaminones, rhodium carbenoids