Some reactions of 2-ethenyl-4,4-Ethylenedioxy-1-methylcyclohex-1-ene prepared by pyrolysis of 5,5-Ethylenedioxy-7a-methyl-4,5,6,7-tetrahydro-2H-inden-1(7aH)-one

Abstract

Flash vacuum pyrolysis of 5,5-ethylenedioxy-7a-methyl-4,5,6,7-tetrahydro-2H-inden-1(7aH)-one (2) at 630º gave a good yield of 2-ethenyl-4,4-ethylenedioxy-1-methylcyclohex-1-ene (6), but at 740º p-cresol was the major product. The diene acetal (6) was also obtained by pyrolysis of 5,5-ethylene- dioxy-lβ-hydroxy-7a-methyl-1,2,5,6,7,7a-hexahydro-4H-indene-1α-carbonitrile (3) at 600º. Pyrolytic reactions of 7a-methyl-2,3,7,7a-tetrahydro-1H-indene-1,5(6H)-dione (1), 5,5-ethylenedithio-7a- methyl-2,3,5,6,7,7a-hexahydro-1H-inden-1-one (7) and of 1,1-ethylenedioxy-3,5,5-trimethylcyclohex- 3-ene (8) are also described.

Mild hydrolysis of the diene acetal (6) afforded 3-ethenyl-4-methylcyclohex-3-en-1-one (9) which upon brief treatment with dry hydrogen chloride in chloroform at 0º gave, after preparative thin-layer chromatography, a low yield of pure 3-ethenyl-4-methylcyclohex-2-en-1-one (11).

The diene acetal (6) failed to undergo Diels-Alder reactions, even at high pressures with Lewis acid catalysts, and it reacted anomalously with two molecules of 4-phenyl-1,2,4-triazoline-3,5-dione; the isomeric diene acetal 1-ethenyl-3,3-ethylenedioxy-6-methylcyclohex-1-ene (18) gave the expected Diels-Alder adduct with this reagent.