Abstract
The photocyclization of 2, 3-dibenzylidenebutyrolactones (5) was investigated in association with the possible biogenetic pathway to natural naphthalide lignans in which 1-phenyl-2, 3-naphthalide types predominate over 4-phenyl-2, 3-naphthalide ones. The butyrolactones (5) were prepared via Stobbe condensation of benzylidenesuccinates (6) followed by the selective reduction of the resulting half esters (7) to hydroxy acids (8) and subsequent lactonization. and their cis, cis-configuration was assigned on the basis of comparative proton magnetic resonance (1H-NMR) data. Irradiation of 5 afforded selectively β-apolignans (11) of the 1-phenyl-2, 3-naphthalide types irrespectively of the ring substituents, and none of the 4-phenyl-2, 3-naphthalide types was formed in the reaction.
