Synthetic Photochemistry. XXXI. The Cycloaddition Reaction of Myrcene with 2,4-Dioxopentanoate : A Facile Synthesis of a Versatile Intermediate for Cycloneryl Derivatives

Methyl 2,4-dioxopentanoate and myrcene smoothly afforded the photoadducts by irradiation with a high-pressure mercury lamp. The (2+2) rr adducts were selectively resulted from the conjugated double bond moiety. Reductive cyclization of the adduct afforded cycloneryl derivatives, whose further chemical conversion were carried out. Previously we have accomplished total syntheses of protoilludenes2' and some elemenoid sesquiterpenoids3' by means of the photocycloaddition of enolized B-diketone with appropriate olefins. Particularly, taking the advantage that the conjugated olefins are capable of forming photocycloadducts with 2,4-Dioxopentanoate (1), 3'`' we have carried out the photocycloaddition with isoprene (A) to efficiently construct the Cio-frameworks3•5' which were convertible to the correct head-to-tail monoterpenoid