[2-FURANONES TO ALKENES - FIRST STEP FOR AN EFFICIENT AND DIASTEREOSELECTIVE SYNTHESIS OF (+)-GRANDISOL AND (-)-GRANDISOL(2] PHOTOCYCLOADDITION OF HOMOCHIRAL 2(5H))

The [2+2] photocycloaddition of homochiral 5-alkyl-2(5H)-furanones to alkenes is studied in order to evaluate the influence of the stereogen ic centre to induce facial diastereoselectivity. The major cycloadduct could be transformed, eventually, in (+)-grandisol. The existence of a charge-transfer complex between the furanone and electron rich subst ituted alkenes as well as the formation of a predominant conformation in 5-oxyalkylfuranones due to n-pi interactions are discussed.