Reactions of polycyclic ketones with Dimethoxycarbene; a convenient route for a one-pot preparation of some alpha-hydroxycarboxylic acid esters

摘要

Polycyclic 'cage' ketones, such as pentacyclo[5.4.0.02,6.03,10.05,9]undecan-8-one (10), pentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-dione (11), and adamantan-2-one (16) were treated with the nucleophilic dimethoxycarbene (DMC; 1), which was generated thermally from 2,5-dihydro-2,2-dimethoxy-5,5-dimethyl-1,3,4-oxadiazole (4a) in boiling toluene. In this 'one-pot' procedure, the ahydroxycarboxylic\udacid ester 12 or a corresponding derivative 15 or 17 was obtained (Schemes 4 – 7).\udAdditionally, 'cage' thione 21 was treated with DMC under the same conditions yielding dimethoxythiirane 22 (Scheme 8). Subsequent hydrolysis or desulfurization (followed by hydrolysis on silica gel) of 22 gave alpha-mercaptocarboxylate 25 and the corresponding desulfurized ester 24, respectively. In all cases, the addition of DMC occurred stereoselectively, and the addition from the exo-face is postulated to explain the structures of the isolated products.