Photochemical synthesis at low temperatures. Part III. Ready synthesis of bicyclo[4,2,0]octan-2-ones from cyclohexenones and ethylene

Abstract

The photochemical [2 + 2] cycloadditions of ethylene to cyclohex-2-en-1-one and 3,5,5-trimethylcyclohex-2-en-1-one at –70° in dichloromethane produce the corresponding bicyclo[4,2,0]octan-2-one derivatives in 90 and 85% yields, respectively, in one step and in preparatively useful amounts. Under the same conditions, or in acetone as solvent at –70°, acetylene does not undergo a [2 + 2] cycloaddition with either ketone.