TETRAHEDRON LE'ITERS Pergamon Tetrahedron Letters 40 (1999) 8705-8709 Enantioselective synthesis of polycyclic ketones by desymmetrisation of bis(phenylsulfonyl)alkenes with chiral alcoholates. Control of the absolute configuration by a simple modification of the chiral auxiliary Sergio Cossu,* Ottorino De Lucchi,* Paola Peluso and Raffaella Volpicelli Dipartimento di Chimica, Universit~ Ca' Foscari di Venezia, Dorsoduro 2137, 1-30123, Venezia, Italy Received 6 August 1999; accepted 28 September 1999 Abstract Treatment of polycyclic bis(phenylsulfonyl)alkenes with chiral alcoholates, followed by acidic work-up, affords enantioselectively ct-phenylsulfonyl ketones. The enantioselectivity is total with monomethylated hydrobenzoin and of opposite configuration with respect to that obtained with hydrobenzoin itself. Thus, starting from a bis(phenylsulfonyl)alkene, it is possible to obtain either the R or S polycyclic ketone by the use of the same chirai auxiliary (hydrobenzoin) and a simple modification (methylation of one of the hydroxy functions). © 1999 Elsevier Science Ltd. All rights reserved. Keywords. desymmetrisation; asymmetric synthesis; polycyclicketones; sulfones. In standard asymmetric synthesis, the production of one or other enantiomer is usually accomplished by using one or other antipode of a chiral auxiliary. In practice, this is not always attainable because most chiral auxiliaries are of natural origin and available largely as only one enantiomer. It follows that, if the use of a chiral auxiliary leads, for example, to the enantiomer of S configuration, the production of the R enantiomer is not always convenient, and a completely different approach has to be frequently undertaken. To solve this problem, several strategies have been put forward that are often based on the change of a key substituent of the chiral auxiliary.1 Here, we report on the switch of configuration that can be obtained in the recently reported procedure for the synthesis of chiral polycyclic ketones, based on the diastereoselective desymmetrisation of bis(phenylsulfonyl)alkenes, z As shown in Scheme 1, the change of configuration was observed when the desymmetrisation reaction, formerly reported with C2- chiral diolates (upper part of Scheme 1), was performed with chiral alcoholates possessing the same backbone configuration (lower part of Scheme 1). The reaction with chiral alcoholates has the additional important advantage of leading directly to enantiomorphic et-phenylsulfonyl ketones (e.g. 4) without * Corresponding authors. 0040-4039/99/$ - see front matter© 1999 ElsevierScienceLtd. All rightsreserved. PII: S0040-4039(99)01848-1