Photo-Cycloaddition of 3-Methoxycyclohexenone and 3-Aminocyclohexenone to Ethoxyethylene : Stereochemistry of the Cycloadducts

Abstract

Irradiation of a methanolic solution of 3-methoxycyclohexenone and ethoxyethylene with 254 nm light gave four stereoisomeric head-to-tail [2+2] cycloadducts in the ratios indicated in Fig. 3. The structure and stereochemistry of all the isomers were determined by chemical correlations and spectroscopic means, respectively. The time-course product analysis suggested that, in this reaction, the exo and endo oriented π-complexes are equally formed, and both give the cycloadducts with a slight preference for antara-selectivity. The analogous cycloadduct of 3-aminocyclohexenone to ethoxyethylene decomposed into 2-ethoxycyclooctane-1, 5-dione on silica gel chromatography.