Silica-Alumina-Supported Amine Catalysts for C-C Bond Formations

Key words

acid-base bifunctional catalysts - silica-alumina support - Michael addition - nitroaldol reaction - cyanoethoxy-carbonylation

Significance

Acid-base bifunctional silica-alumina-supported amine catalysts (SA-NEt₂ and SA-NH₂) were prepared and applied to the carbon-carbon bond-forming reactions. Thus, SA-NEt₂ was prepared from an amorphous silica-alumina (SA) N633HN (SiO₂: 66.5%; Al₂O₃: 25.1%; 380 m²g^-1) and 3-(diethylamino)propyl trimethoxysilane in toluene under reflux conditions. The cyanoethoxycarbonylation of 1 with 2 was catalyzed by SA-NEt₂ to give the corresponding carbonates 3 in 88-99% yield (12 examples). The Michael reaction of 4 and 5 was performed with SA-NEt₂ to give the corresponding adducts 6 in 94-99% yield (3 examples). SA-NH₂-promoted the nitroaldol reaction of 7 and 8 to afford the nitroalkenes 9 in 88-99% yield (4 examples).

Comment

SA-NEt₂ and SA-NH₂ were reused four times without loss of catalytic activity in Michael and nitroaldol reactions. ¹H NMR spectroscopic analysis of the filtrate of the reaction mixture showed no leaching of amine compounds. SA-NEt₂ and SA-NH₂ were characterized by solid-state ¹³C and ²⁹Si NMR spectroscopy, FT-IR spectroscopy, and elemental analysis. The authors emphasized that the co-existence of acidic and basic sites at the same solid surface without neutralization realized the catalyses with high efficiency.