Convenient synthesis of perhydroindene derivatives from 2,7-dimethyl-1,3,7-octatriene

Abstract

Several perhydroindene derivatives were prepared from 2,7-dimethyl-1,3,7-octatriene (I) via Diels Alder reaction followed by cyclisation. For example, the Diels Alder reaction between I and methyl vinyl ketone (II) in the presence of Lewis acid afforded 4-acetyl-3-(3-methylbut-3-enyl)-1-methylcyclohexene (IIIa), which, upon treatment with phosphoric acid, was converted to a mixture of 2-acetyl-5,7,7-trimethyl-bicyclo [4,3,0]-non-1-(6)-ene (IV), 2-acetyl-5,7,7-trimethylbicyclo[4,3,0]-non-1-ene (VI) and 2-isopropyl-3,6-dimethylindene (V).