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 the alpha or beta-face (beta-face: obtention of the expected acetyl derivatives; alpha-face: presence of aldehydes, anti-Markovnikov addition) may be rationalized by an intramolecular coordination of the metal with the two lactonic oxygen atoms. Calculations carried out using ZINDO I method confirm the existence of such a chelation and the possibility of a cis-hydroxy or a cis-acetoxypalladation in the course of the Wacker process. An experimental confirmation was given by the regioselective mono-oxidation of the vinyl group syn to the methoxycarbonyl group of (3R*,6S*,9S*)-3-methoxycarbonyl-3-(2-propyl)-6,9-divinyl-1-oxaspiro[4.4]nonan-2-one. (C) 1997 Published by Elsevier Science Ltd.