Abstract
We report an enantioselective approach to tertiary α-chloro esters through the reaction of silyl ketene acetals and N-chlorosuccinimide. The reaction is promoted by a chiral squaramide catalyst, which is proposed to engage both reagents exclusively through non-covalent interactions. Application of the tertiary chloride products in stereospecific substitution reactions is demonstrated.
Highlights
We report an enantioselective approach to tertiary α-chloro esters through the reaction of silyl ketene acetals and N-chlorosuccinimide
Among the various subclasses of chiral dual hydrogen bond donors that have been developed over the past decade, tert-leucinearylpyrrolidine derivatives with the general structure in 3–5 have proven remarkably effective in a wide range of enantioselective catalytic reactions
Reactions carried out in dichloromethane (DCM)) afforded racemic product, as NCS is fully soluble in that medium and the chlorination reaction appears to occur entirely through an uncatalyzed pathway
Summary
We report an enantioselective approach to tertiary α-chloro esters through the reaction of silyl ketene acetals and N-chlorosuccinimide. The chlorination of cyclic silyl ketene acetal 1a with N-chlorosuccinimide (NCS) was investigated as a model reaction (Table 1).[10] Among the various subclasses of chiral dual hydrogen bond donors that have been developed over the past decade, tert-leucinearylpyrrolidine derivatives with the general structure in 3–5 have proven remarkably effective in a wide range of enantioselective catalytic reactions. Whereas promising results were observed with thiourea catalyst 3, substantially higher reactivity and enantioselectivity were obtained with the analogous urea and squaramide derivatives 4 and 5a (entries 1–3).
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