The chemistry of terpenes. Part XVII. Synthesis of (+)-cis-homocaronic acid (cis-3-carboxymethyl-2,2-dimethylcyclopropanecarboxylic acid) and some related compounds

Abstract

Ozonolysis, in methanol, of (+)-4α-actoxymethylcar-2-ene (7), decomposition of the ozonide with alkaline hydrogen peroxide, and esterification of the acidic products with diazomethane gave principally dimethyl (+)-cis-homocaronate (methyl-cis-3-methoxycarbonylmethyl-2,2-dimethylcyclopropanecarboxylate)(4; R = Me) and (+)-cis-1-methoxycarbonyl-2,2-dimethyl-3-(3-oxobutyl)cyclopropane (9). Also formed were (+)-cis-1-methoxycarbonyl-2,2-dimethyl-3-[(1-acetylcyclopropyl)methyl]cyclopropane (10), (+)-cis-1-methoxycarbonyl-2,2-dimethyl-3-(2-methoxymethyl-3-oxobutyl)cyclopropane (11) as a pair of epimers, and (+)-cis-1-methoxycarbonyl-2,2-dimethyl-3-(2-methylene-3-oxobutyl)cyclopropane (12). (+)-cis-1-Methoxycarbonyl-2,2-dimethyl-3-[(2-acetyloxiran-2-yl)methyl]cyclopropane (18) is a precursor of (+)-cis-homocaronic ester. Ozonolysis, in methanol, of (+)-4α-acetylcar-2-ene (8) and treatment of the product as described for (7) also yielded (+)-cis-homocaronic ester, but the principal product was (+)-cis-1-methoxycarbonyl-2,2-dimethyl-3-(2-methoxycarbonlypropyl)cyclopropane (27). Ozonolysis of the ketone (8) in acetic acid or in pyridine gave (+)-cis-1-methoxycarbonyl-2,2-dimethyl-3-(2,2-diacetylethyl)cyclopropane (28), which was oxidised with alkaline hydrogen peroxide to (+)-cis-homocaronic acid.