NH₂SO₃H–SiO₂ as a new water‐compatible, recyclable heterogeneous catalyst for the synthesis of novel (α,β‐unsaturated) β‐amino ketones via aza‐Michael reaction

Abstract

NH 2 SO 3 H-SiO 2 as a new water-compatible, recyclable heterogeneous catalyst for the synthesis of novel (α,β-unsaturated) β-amino ketones via aza-Michael reaction Zeba N. Siddiqui* and Nayeem Ahmed NH 2 SO 3 H-SiO 2 /water as a novel catalytic system was used for the synthesis of (α,β-unsaturated) β-amino ketones via aza-Michael reaction at reflux conditions. The methodology was of general applicability and the catalyst exhibited activity up to five cycles. The catalyst was characterized for the first time using FT-IR, X-ray diffraction and scanning electron microscopic-energy dispersion analytical X-ray. The stability of the catalyst was evaluated by differential scanning calorimetry and TGA/differential thermal analysis. High efficiency of the catalyst along with its recycling ability and the rather low loading demonstrated in reactions are the merits of the presented protocol.

A convenient synthesis of coumarinyl chalcones using HClO4–SiO2: A green approach

“…Thus, based on the above findings and in continuation of our interest for the synthesis of coumarin and chalcone derivatives (Siddiqui and Ahmed., 2013;Siddiqui et al, 2008) we report herein, the use of silica supported perchloric acid (HClO 4 -SiO 2 ) as a mild, highly efficient, and recyclable heterogeneous catalyst for the synthesis of coumarin based chalcones under thermal solvent-free conditions in excellent yields.…”

Lanthanum immobilized on chitosan: a highly efficient heterogeneous catalyst for facile synthesis of novel (α,β‐unsaturated) β‐aminoketones

“…Elimination of NH(CH 3 ) 2 group from II leads to the formation of 3a , 3b , 3c , 3d , 3e , 3f , 3g . The intermediate III undergoes cyclization and expulsion of NH(CH 3 ) 2 group to form imine intermediate IV which isomerizes to afford products 3h , 3i , 3j via a Dimroth‐type rearrangement …”

“…The intermediate III undergoes cyclization and expulsion of NH(CH 3 ) 2 group to form imine intermediate IV which isomerizes to afford products 3h-j via a Dimroth-type rearrangement. [21,26] …”

“…H 2 SO 4 , Mg-Al hydrotalcites and silica-supported sulfamic acid. [18][19][20][21] A few drawbacks associated with these protocols include the use of homogeneous and corrosive catalysts and limited substrate tolerance. [18,19] In this regard, protocols for the synthetic improvement of this reaction are still desirable.…”

“…To our knowledge, only a few reports are available in the literature of aza‐Michael reactions of β‐enaminones using AcOH, conc. H 2 SO 4 , Mg–Al hydrotalcites and silica‐supported sulfamic acid . A few drawbacks associated with these protocols include the use of homogeneous and corrosive catalysts and limited substrate tolerance .…”