39 ShionaneおよびFriedelane誘導体の骨格転位反応

概要

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Boron rifluoride etherate-catalyzed backbone rearrangement of 3α,4α-epoxyshionane (7), 3β,4β-epoxyfriedelane (32), and 3β,4β-epoxyshionane (8) was investigated. Rearrangement of D-homo-steroidal epoxide (25) and bicyclic epoxybenzoate (30) was also accomplished. 3α,4α-Epoxyfriedelane (18) or 7 gave 5(10)-en-3α-ol (19 or 14) of D: B-friedo-type and 12-en-3α-ol (21 or 12) in which backbone rearrangement was highly effected, while 25 yielded only 27. The formation of rearranged products (19-23) from 18 has already been reported. Bicyclic epoxybenzoate (30), as a model of A/B ring part of friedelane and shionane type triterpenes, gave cyclic etherbenzoate (31) upon treatment with boron trifluoride etherate. Two epoxides (32 and 8) reacted with boron trifluoride etherate in ether at low temperature to afford dendropanoxide (33) and dihydrobaccharis oxide (2), respectively. Each of these epoxides (32 or 8) also produced 4α-fluoro-3β-ol (34 or 38), 5-en-3β-ol (36 or 39), 5(10)-en-3β-ol (35 or 15), 12-en-3β-ol (37 from 32), and 7-en-3β-ol (40 from 8). The epoxide (8) was found to rearrange into 39, 15, 42, 40, and 10 in benzene at room temperature. The relative yields of the products afforded by the rearrangement in various solvents are shown in the Table.
天然有機化合物討論会の論文
1976-09-20