ANION REACTIONS OF 1,3-DITHIANE 1,3-DIOXIDE WITH CARBONYL-COMPOUNDS -HIGH DIASTEREOSELECTIVITY WITH AROMATIC-ALDEHYDES UNDER CONDITIONS OFEQUILIBRIUM CONTROL

We have investigated the anion chemistry of trans-1,3-dithiane 1,3-dio xide (4) with aldehydes and ketones, and we have found that this reage nt undergoes highly selective addition reactions with aromatic aldehyd es but only when reactions are under equilibrium control (achieved usi ng Na anion of 4). Other metals invetsigated (Li, Mg, Al, Ce, Ti) gave either poorer selectivity or caused decomposition of 4. Zn-4 did give improved selectivity at low temperature but only with aromatic aldehy des. Reactions with ketones were limited to those without a-branching. A model that accounts for the high diastereoselectivity observed with aromatic aldehydes is presented.