Flash vacuum pyrolysis of 5,5-ethylenedioxy-7a-methyl-4,5,6,7-tetrahydro-2H-inden-1(7aH)-one (2) at 630� gave a good yield of 2-ethenyl-4,4-ethylenedioxy-1-methylcyclohex-1-ene (6), but at 740� 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 600�. 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 0� 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.
The reaction of 3-ethenyl-4-methylcyclohex-2-en-1-one (4) with 2-methylcyclopentane-1,3-dione in refluxing toluene containing pyridine gave 6% of 9bξ-hydroxy-3a,6-dimethyl-3a,4,5,6,7,9b-hexahydro-1H-benz[e]indene-3,9(2H,8H)-dione (10). When the same reactants were heated at 100-110� (sealed tube) in benzene containing t-butyl alcohol and diethylamine the main product (61%) was 5',6-dimethylspiro[bicyclo[3.2.1]octane-1,2'-cyclohexane]-3,6',8'-trione (11); the yield of (11) was 72% when the reaction was carried out in the presence of silica gel. Attempts to effect a similar reaction of the dienone (4) with methyl 1β-t-butoxy-7aβ-methyl-5-oxo-1,2,3,3aα,4β,6,7,7a-octahydro-indene-4-carboxylate (21a) gave no conjugate Michael addition product, but (21a) underwent aminolysis to the corresponding diethylamide (21b). Attempts to alkylate the t-butoxy β-keto ester (21a) under various conditions with 7-acetyloxy-7-ethenyl-8 ξ methyl-1,4-dioxaspiro[4,5]decane (41) failed. Similarly, attempts to effect alkylation of the anion of the t-butoxy keto ester (21a) with 7-ethenyl-8-methyl-1,4-dioxaspiro[4,5]dec-6-ene (43) under Lewis acid catalysis were also unsuccessful.