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3.4.3.2 Metal-Complex-Catalyzed Addition in C—N Bond Formation

DOI: 10.1055/sos-SD-206-00122

Mase, N.Science of Synthesis: Water in Organic Synthesis, (20121195.

As noted in Section 3.4.3.1, in general a high temperature is required for aqueous conjugate addition of amine nucleophiles to electron-deficient alkenes in the absence of a catalyst. However, this reaction can be achieved at room temperature in the presence of a Lewis acid catalyst. Tin(IV) chloride (10mol%),[‌109‌] ammonium cerium(IV) nitrate (CAN; 3mol%),[‌110‌] polyaniline-supported indium(III) chloride (PANI-In; 10mol%),[‌111‌] and 12-tungstophosphoric acid (H3PW12O40; 1mol%)[‌112‌] have been found to be efficient catalysts for promoting conjugate addition reactions of amines 151 to electron-deficient alkenes 150 such as α,β-unsaturated esters, acrylamide, and acrylonitrile in water (Scheme 42). However, with respect to the scope of substrate and commercial availability, boron compounds are the recommended catalysts. Borax[‌113‌] and boric acid[‌114‌] efficiently catalyze the conjugate addition reaction of amines 151 to α,β-unsaturated aldehydes, ketones, esters, amides, and nitriles under aqueous conditions to afford the corresponding β-amino Michael adducts 152 in good yields at room temperature. The aqueous layer containing boric acid is reused for the next run. Borax and boric acid are efficient catalysts with aliphatic amine nucleophiles, but not with aromatic amines; on the other hand, 12-tungstophosphoric acid (H3PW12O40) is a suitable catalyst with aromatic amine nucleophiles.[‌112‌]

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