The acid-induced reaction of rigid p, r-or y-&unsaturated methyl ketones with methyl orthoformate is shown to yield alkenylcyclopentenones and-cyclohexenones, respectively. The use of ethyl orthoformate leads to more complex ring structures incorporating an ethoxy unit in both carbon-oxygen and carbon-carbon bonded form. The new structures are determined by 13C NMR spectroscopy and their formation is justified on the basis of ...
