GENERATION AND ALKYLATION OF ALPHA-LITHIO-SE,O-HETEROACETALS, AND STEREOSELECTIVE CYCLIZATION OF OLEFINIC SE,O-HETEROACETALS

Generation of alpha-lithio-Se,O-heteroacetals was accomplished by dire ct deprotonation of O-methoxyethylselenoacetals with lithium 2,2,6,6-t etramethylpiperidide. Alkylation of the alpha-lithioheteroacetals smoo thly proceeded to give the products 6 and 7. Olefinic Se,O-heteroaceta ls 6c and 6d were cyclized via alpha-seleno carbenium ions generated b y selective C-O bond cleavage with titanium tetrachloride to provide t he cyclohexane derivatives 8a and 8b, respectively.