photocycloaddition reaction (λ = 254 nm, solvent: diethyl ether or tert-butyl alcohol) was carried out in an intramolecular fashion the tri- and tetracyclic products 21−23, 27−36 were obtained in good yields (52−75%) and with excellent simple diastereoselectivity. The reaction tolerates a high degree of substitution at both the tetronate and at the alkene double bond. High facial diastereoselectivities were observed