Cyclodimerization of the Stevens Rearrangement Products from 4-Alkoxy-2-butynyl(alkoxycarbonylmethyl)dimethyl-ammonium Salts into Cyclohexene Derivatives

4-Alkoxy-2-butynyl(alkoxycarbonyl)dimethylammonium salts undergo 3,2-Stevens rearrangement by the action of the corresponding sodium alkoxides. Hydrolysis of the rearrangement products with dilute hydrochloric acid gives 3-alkoxy-2-oxo-3-pentenoic acid esters which are converted into 3-methylene-2-oxo-4-pentenoates via 1,4-elimination of alcohol. [2 + 4]-Cyclodimerization of 3-methylene-2-oxo-4-pentenoates leads to 1,4-bis(alkoxalyl)-4-vinylcyclohexenes.