REGIOCHEMISTRY OF WACKER-TYPE OXIDATION OF VINYL GROUP IN THE PRESENCE OF NEIGHBORING OXYGEN FUNCTIONS .2.

The regioselectivity of the palladium(II) oxidation of (+/-)-17 alpha- vinyl-1,3,5(10)-gonatriene derivatives bearing a lactonic bridge on th e alpha or beta-face (beta-face: obtention of the expected acetyl deri vatives; alpha-face: presence of aldehydes, anti-Markovnikov addition) may be rationalized by an intramolecular coordination of the metal wi th the two lactonic oxygen atoms. Calculations carried out using ZINDO I method confirm the existence of such a chelation and the possibilit y of a cis-hydroxy or a cis-acetoxypalladation in the course of the Wa cker process. An experimental confirmation was given by the regioselec tive mono-oxidation of the vinyl group syn to the methoxycarbonyl grou p of (2-propyl)-6,9-divinyl-1-oxaspiro[4.4]nonan-2-one. (C) 1997 Publi shed by Elsevier Science Ltd.