63(PA2-3) ジビニルカルビノール誘導体の不斉エポキシ化反応を利用するマイコとキシン類の合成(ポスター発表の部)

概要

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Titanium-tartrate mediated asymmetric epoxidation of (4) proceeded with high diastereoselectivity and enantioselectivity (>95% ee) giving rise to (5). The epoxide (5) was then converted to (14) using the diastereoselective allylic alkoxy directed hydroxylation (diastereoselectivity: 15: 1). Acid catalyzed cyclization of (14) took place regio- and stereo-selectively to give the tetrahydrofuran derivative (15) which was converted to (+)-citreoviral (28) through assembly of the C-2 side chain and inversion of the C-3 cofiguration. The synthesis of (28) constitutes a formal synthesis of citreoviridin (8). Furthermore, it was found that treatment of (29) with tin tetrachloride in methylene chloride at -50℃ afforded the tetrahydrofuran derivative (33) and the oxetane (31) in a ratio of 3: 1 in good yield. The tetrahydrofuran derivative (33) was similarly transformed into the α,β-unsaturated ester (38) whose structure was confirmed by comparison with the key intermediate of the Yamamura's verrucosal synthesis after transesterification to (39). In conclusion, we have developed an effective chiral route to highly functionalized tetrahydrofuran systems which constitute the characteristic subunits of mycotoxins such as citreoviridin (8) and verrucosidin (10), using the titanium-tartrate mediated asymmetric epoxidation of a prochiral divinylcarbinol having a σ-symmetrical nature.
天然有機化合物討論会の論文
1987-07-25