title: Photochemical, thermal, and base-induced access to hydroazulene derivatives via two-carbon ring-enlargement reactions of condensed electrophilic cyclobutenes.
abstract: Enamines, silyl enol ethers, and beta-keto ester anions derived from bicyclo[3.3.0]octan-2-one efficiently underwent a formal [2 + 2] cycloaddition reaction with DMAD and ethyl propynoate leading to a large variety of electrophilic cyclobutenes. The latter were transformed into polyfunctionalized bicyclo[5.3.0]decane (or hydroazulene) ring systems in high yields by fragmentation of the cyclobutene moiety. These two-carbon ring-enlargement reactions were utilized as a synthetic tool for the construction of a polyfunctionalized hydroazulene derivative that represents a potential precursor of the tricyclic framework of ingenol.
authors.affiliation: Laboratoire de Chimie Organique Synthétique (UMR 7123 CNRS), Faculté de Chimie, Université Louis Pasteur 1, rue Blaise Pascal, BP 296/R8, F-67008 Strasbourg Cedex, France.
authors.forename: Gaëtan L
authors.initials: GL
authors.lastname: Mislin
authors.forename: Michel
authors.initials: M
authors.lastname: Miesch