Synthesis of Racemic β-Chamigrene, a Spiro[5.5]undecane Sequiterpene

The present paper describes a total synthesis of racemic β-chamigrene (1), a sesquiterpene with a spiro[5.5]undecane carbon framework. Compared with previously reported β-chamigrene syntheses, we were able to reduce the total number of reaction steps, which also resulted in a significant improvement of the overall yield. The commercially available ketone 6-methylhept-5-en-2-one was transformed by known simple procedures into 3,3-dimethyl-2-methylenecyclohexanone. This reacted with isoprene by a Diels-Alder reaction to give a spiro ketone. An olefination reaction on this compound gave the target molecule

Small-Ring Compounds. XVIII. Alkali-induced Ring Opening of Some Phenylcyclobutenone Derivatives

Phenylcyclobutenedione (I) has been found to decompose by the action of alkali to benzylidenepyruvic acid (X) and benzaldehyde. Similarly 2-hydroxy-3-phenyl-2-cyclobutenone (V) yields benzylpyruvic acid (VII), and 4-hydroxy-3-phenylcyclobutenedione (XI) gives phenylpyruvic acid (XII) and 1,3-diphenylpropene (XIII). Possible reaction mechanisms for the formation of these substances are proposed