Asymmetric addition of an electrophile to naphthalenes promoted and stereodirected by alcohol

4-Phenyl-1,2,4-triazoline-3,5-dione (PTAD) reacts with 1 -methoxy-4-methyln aphthalene to give the 1,4-addition product in the presence of methanol; th e reaction does not proceed in the absence of the alcohol. Methoxy exchange (with CD3OD) was also observed during the reaction. Reactions of PTAD with 1-(3-hydroxypropoxy)-4-methylnaphthalene and related naphthalenes afford s tereoselectively 1,4-adducts (70-98% of the major diastereomer). The stereo face-selective addition of PTAD at C-4 with concurrent formation of an acet al at C-1 takes place in a syn manner, which is induced by the hydrogen-bon ding interaction between PTAD and the hydroxy group. The alpha -methyl subs titution on the propoxy side chain strongly enhances the stereodifferentiat ion (90% de) and accelerates the cyclization by the Thorpe-Ingold effect. T he alkoxy moiety of the adduct is easily removed to give 4-methyl-4-amino-4 H-naphthalen-1-one with high enantiomeric excess. The gamma -methyl group o f the side chain also affects the stereodifferentiation. Thus, the two ster eogenic centers of the (1S,3R)-3-hydroxy-1-methylbutoxy side chain work tog ether to achieve the high stereodifferentiating 1,4-addition from the Si-Re face (up to 96% ee). Epimerization of the cyclic acetal of a minor adduct was observed during the reaction of 1-(3-hydroxybutoxy)-4-methylnaphthalene , indicating that the minor component of the final products is derived from the initial minor syn adduct formed from the opposite face. The syn select ivity of the addition is achieved completely in the initial stage of format ion of both the major and the minor adducts.