Enantioselective formal synthesis of (+)-dihydrocorynantheine and (-)-dihydrocorynantheol.

Mercedes Amat, Arantxa Gómez-Esqué, Carmen Escolano, Maria M M Santos, Elies Molins, Joan Bosch

Index: J. Org. Chem. 74(3) , 1205-11, (2009)

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Abstract

The enantioselective construction of the 3-ethylindolo[2,3-a]quinolizidine moiety present in numerous indole alkaloids is reported, the key steps being a stereoselective cyclocondensation of (S)-tryptophanol with an appropriate racemic delta-oxoester and a regio- and stereoselective cyclization of the resulting oxazolopiperidones on the lactam carbonyl group. A new procedure for the removal of the hydroxymethyl auxiliary group, involving oxidation to an aldehyde, dehydration of the corresponding oxime, and reductive decyanation of the resulting alpha-aminonitrile, has been developed. The preparation of indoloquinolizidine 27 represents a formal total synthesis of (+)-dihydrocorynantheine, (-)-dihydrocorynantheol, and other indolo[2,3-a]quinolizidine and oxindole alkaloids bearing the same substitution pattern.