Exploration into Double Nucleophilic Addition Reaction to α, β- Unsaturated Aldimines Promoted by Titanium Tetrahalides

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In the present study, we found that in the presence of a titanium tetrahalide, ketene silyl acetals underwent 1,4- and subsequently 1,2-addition to α, β-unsaturated aldimine to give doubly alkylated products in good yields. The reaction of a mixture of a ketene silyl acetal and an allyltributylstannane with α,β-unsaturated aldimine gave regio- and chemoselectively 1,4- and 1,2-doubly alkylated product, in which the ketene silyl acetal underwent 1,4-addition while the allyltributylstannane underwent 1,2-addition. Moreover, in the presence of AlCl_3 and MS 4A containing H_2O, ketene silyl acetals underwent 1,4- and then 1,2-addition with α,β-unsaturated imines to give doubly alkylated products in good yields with high diastereomeric excesses. A mixture of thiols and tetraallyltin also underwent 1,4- and 1,2-addition, respectively, with α, β-unsaturated imines with TiCl_4, to give 6-sulfenyl-4-amino-1-alkenes in good yields.