Diastereoselective Tandem Michael−Intramolecular Wittig Reactions of a Cyclic Phosphonium Ylide with 8-Phenylmenthyl Enoates

Abstract

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 4a afforded (3R,4S)-4-(diphenylphosphinyl)-3-phenylcycloheptanone (3R,4S)-5a as the major isomer. The diastereoselectivity of the initial tandem reactions was estimated to be 94:6 from the 31P NMR of a mixture of the diastereomeric ketal derivatives 6a and 6'a which were obtained by the reaction of 5a 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 5b-d were obtained and that the diastereomer ratios of their ketal derivatives were 60:40-73:27.

Domino Reaction of Pyrrolidinium Ylides: Michael Addition/[1,2]-Stevens Rearrangement

“…Domino reactions provide an opportunity to synthesize in one step relatively complicated products from simple precursors. − Many well-known domino transformations are initiated by the Michael-type addition. ,− Among anions undergoing a conjugate addition to electrophilic alkenes are sulfonium, ,− sulfoxonium, ,, arsonium, − ,, telluronium, ,,, phosphonium, ,, pyridinium, , and ammonium ,,,, ylides, generated from respective salts upon treatment with a base. The anionic intermediates thus formed usually take part in Michael-initiated ring-closure (MIRC) reactions, affording cyclopropanes or undergoing other transformations, ,,− , giving unexpected products, − mainly dihydrofuran and benzofuran derivatives. ,,,,− …”