PHOTOCYCLOADDITION OF VARIOUS KETONES AND ALDEHYDES TO VINYL ETHERS AND KETENE DIETHYL ACETAL

Photoaddition of acetone to ethyl, n-butyl, and isobutyl vinyl ether and of propionaldehyde, cyclohexanone, benzaldehyde, and benzophenone to ethyl vinyl ether gives the corresponding 2- and 3-alkoxyoxetanes in ratios of (25 ± 5):75 independent of solvent. Acetone, cyclohexanone, and benzophenone also add to ketene diethyl acetal to give 2,2- and 3,3-diethoxyoxetanes in analogous ratios. Only 3,3-dialkoxyoxetanes were obtained from the photochemical reaction of ketene diethyl acetal with propion- and benzaldehyde. Selective transformations of 2-alkoxy- and 2,2-dialkoxyoxetanes with water, alcohols, or lithium aluminum hydride are used as a means of analyzing the reaction mixtures. The directions of the cycloadditions are compared with those of radical additions to vinyl ethers and ketene acetals. It is concluded that the isomer ratios in the cycloadditions cannot simply be predicted from the energy differences of the possible intermediates. © 1969, American Chemical Society. All rights reserved.