Photolysis (λ = 254 nm) of 4-(t-Bu)-substituted [b]-fused bi- and tricyclic pyrandiones 5 affords title compounds 4 in good yields as well as small amounts of spiroalkanediones 8. The alkyl-substitution pattern at C(4) of the pyran ring in 5 determines the relative amount of α vs. β-cleavage products obtained from the primarily formed acyl-vinyloxy biradical.
                                    4-(t- Bu)-取代的[ b ]稠合的双环和
三环吡喃二酮5的光解(λ= 254 nm)提供了高收率的标题化合物4以及少量的螺旋烷二酮8。5中
吡喃环的C(4)处的烷基取代模式决定了从最初形成的酰基-
乙烯基氧基双自由基获得的α对β裂解产物的相对量。