Highly efficient mesoporous base catalyzed Knoevenagel condensation of different aromatic aldehydes with malononitrile and subsequent noncatalytic Diels–Alder reactions

Abstract

Knoevenagel condensation and [4 + 2] cycloaddition reactions are very important class of reactions in synthetic organic chemistry. We have prepared amino-functionalized mesoporous silica through co-condensation of 3-aminopropyltriethoxy-silane (APTES) along with tetraethylorthosilicate (TEOS) in presence of a cationic surfactant CTAB hydrothermally. Small angle powder XRD, HR TEM, FE SEM, N 2 sorption and FT IR spectroscopic tools are used to characterize the 2D-hexagonal mesostructure and to identify the presence of surface –NH 2 groups in amino-functionalized mesoporous silica material. Our experimental results reveal that amino-functionalized mesoporous silica is an efficient base catalyst for the Knoevenagel condensation of different aromatic aldehydes with malononitrile to α,β-unsaturated dicyanides under very mild reaction condition and in the presence of ethanol solvent. The isolated α,β-unsaturated dicyanides obtained through the condensation reaction further react very efficiently with cyclopentadiene to form a series of Diels–Alder cycloaddition products in excellent yields in the absence of any catalyst.