79 ラクトンエノールトリフレートを経由する天然物合成(口頭発表の部)

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Since past two decades ago, more than fifty compounds including medium-sized cyclic ether ring systems have been isolated from marine algae, Laurencia species. These could be structurally attractive synthetic targets. We describe the preliminary results of a new synthetic strategy aimed to these natural products involving conversion of lactones into substituted cyclic ethers via enol trifluoromethanesulfonates (triflates). A general procedure is as follows: To a solution of lactone in tetrahydrofuran (THF) was added a solution of lithium hexamethyldisilazide in THF and hexamethylphosphoric triamide (HMPA) at -78℃, and the solution was stirred at -78℃ for 2 h. A solution of N-phenyl triflimide in THF was then added and the mixture was stirred at 0℃ and 20℃ for 2 h. Usual work up yielded the crude enol triflate, which is stable in the presence of a trace amount of HMPA. The data in Table 1 indicate that six- or seven-membered lactones could be converted efficiently to the corresponding enol ethers, while the reaction with eight-membered lactones proceeded only in the case of unsaturated systems. Enol triflates obtained thus were smoothly coupled with various lithium dialkylcuprates to give the corresponding alkylated cyclic enol ethers (Table 2). This strategy was effectively applied to N-protected-δ-lactams (Table 3), and then to the synthesis of (+)-lauthisan (2)(Scheme 1). Its application to the synthesis of (+)-laurencin (1) is now in progress (Scheme 2).
天然有機化合物討論会の論文
1990-09-25

79 ラクトンエノールトリフレートを経由する天然物合成(口頭発表の部)

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