SOLVENT EFFECT ON THE BACKBONE REARRANGEMENT OF 3β,4β-EPOXYSHIONANE CATALYZED BY BORON TRIFLUORIDE ETHERATE

Abstract 3β,4β-Epoxyshionane (3) was treated with BF3–Et2O in ether to give D:B-friedo-bacchar-5-en-3β-ol (7), D:B-friedo-bacehar-5(10)-en-3β-ol (8), D:C-friedo-bacchar-7-en-3β-ol (9), and 4α-fluoroshionan-3β-ol (10), besides previously reported dihydrobaccharis oxide (1), while the reaction in the solvents such as nitromethane, benzene, toluene, hexane, and acetonitrile gave no 1. In the reaction in THF at room temperature, the D:B-friedo-type products (7 and 8) were formed predominantly. The rearrangement in solvents with low nucleophilicity proceeded up to C/D rings; e.g. the reaction in nitromethane at room temperature yielded bacchar-12-en-3β-ol (2) and D:C-friedo-bacchar-8-en-3β-ol (11). The reaction product ratio in the same reaction in various solvents are listed in TABLE.