Synthesis of Chiral 2-Aryl-4-piperidones

The synthesis of chiral 2-(2-indoly1)-and 2-(3-indoly1)-4piperidones by reaction of ~,N-dimethyl-4-oxo-2-[l-(phenylsulfon~l)indolyl]piperidinium iodide and (4-(-)-phenylglycinol is reported.Some years ago we developed an improved synthesis of 2-aryl-4-piperidones which has been applied to the synthesis of a large number of compounds related to natural products and pharmacologically active compounds.1~2However, until now there is no suitable way described to prepare chiral 2-aryl-4-piperidones, even if very recently, the synthesis of chiral 4-piperidones by the use of a rarely employed reaction between N,Ndimethyl-4-oxopiperidinium iodide and (S)-(-)-a-methylbenzylamine has been reported.3In this paper we describe the application of this methodology using (R)-(-)-phenylglycinol and 2-arylpiperidinium salts ( 2) to obtain chiral 2-[I-(phenylsulfonyl)-2-indolyll-and 2-[I-(phenylsulfony1)-3-indolyll-4-piperidones (la) and (1 b) (Scheme 1).Scheme 1