Two [2+2] photocycloaddition routes were evaluated as possible ways to access the tricyclic core structure found in the terpene monoglycoside lactiflorin. While the first route via ?-substituted cyclopentenones was quickly discarded, the reactions of racemic (5R*)-3-benzyloxy-5-but-3'-enyl-4-methoxycarbonylfuran-2(5?H)-ones proceeded in high yields and with perfect diastereoselectivity. However, it turned out that the regioselectivity was strongly dependent on the substitution pattern within the but-3'-enyl chain, which connects the terminal olefinic double bond to the photoexcited butenolide chromophor. If the chain was unsubstituted or if a tert-butyldimethylsilyloxy group was placed at the 2' position in a syn-relationship to the existing stereogenic center (5R*,2'S*), the crossed product prevailed with regioselectivities of 89:11 to 69:31. If the tert-butyldimethylsilyloxy group was positioned at 2' in an anti-relationship to the existing stereogenic center (5R*,2'R*), the desired straight products were obtained in regioselectivities of 74:24 to 55:45 (6183?     «

Two [2+2] photocycloaddition routes were evaluated as possible ways to access the tricyclic core structure found in the terpene monoglycoside lactiflorin. While the first route via ?-substituted cyclopentenones was quickly discarded, the reactions of racemic (5R*)-3-benzyloxy-5-but-3'-enyl-4-methoxycarbonylfuran-2(5?H)-ones proceeded in high yields and with perfect diastereoselectivity. However, it turned out that the regioselectivity was strongly dependent on the substitution pattern within the...     »