SYNTHESIS OF SESQUITERPENS BASED ON A UNIQUE REACTION OF CYCLIC PHOSPHONIUM YLIDES

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The diastereoselective tandem Michael-intramolecular Wittig reactions of a five-membered cyclic phosphonium ylide 2 using 8-phenylmenthyl enoates were examined. The reaction of the phosphonium ylide with 8-phenylmenthyl cinnamate followed by the hydrolysis of the resulting enol ether afforded (3R,4S)-4-(diphenylphosphinyl)-3-phenyl cycloheptanone as the major isomer. The diastereoselectivity of the initial tandem reactions was estimated to be 94 : 6 from the ^<31>P NMR of a mixture of the diastereomeric ketal derivatives which were obtained by the reaction of (3R,4S)-4-(diphenylphosphinyl)-3-phenyl cycloheptanone with (2R,3R)-2,3-butanediol, and the absolute configuration of the major isomer was determined by the single crystal X-ray analysis. Similar reactions using some 8-phenylmenthyl alkenoates were attempted. As a result, it was clarified that the corresponding trans-ketones were obtained and that the diastereomer ratios of their ketal derivatives were 60 : 40-73 : 27. On the other hand, reactions of five and six membered cyclic phosphonium aza-ylides with phenyl thiobenzoate and aryl thiocinnamate gave acylated products. On the other hand, the reactions of cyclic phosphonium aza-ylides with phenyl alkenylthioesters gave com enamino phosphine oxide derivatives. Furthermore, the reactions of five-and six-membered cyclic iminophosphoranes, with β-dicarbonyl compounds gave enamino phosphine oxide derivatives in good yields. The enamino phosphine oxide were stereoselectively converted to 1,6- and 1,7-dienes.