Gold Nanoparticle Functionalized Mesoporous Silica-Chitosan as Efficient and Recyclable Catalyst for the Green One-Pot Synthesis of 4H-pyran Derivatives in Aqueous Medium

Gold nanoparticle functionalized mesoporous silica-chitosan (Au NPs/silica-chitosan) as an environmentally benign and heterogeneous nanocatalyst was prepared and its properties were characterized using field emission scanning electron microscopy (FE-SEM) and fourier transform infrared (FT-IR). The catalytic activity of Au NPs/silica-chitosan was studied in the synthesis of biologically important 4H-pyran derivatives. In these reactions, efficient and green syntheses of 4H-pyrans were carried out using isatins or aldehydes, active methylene compounds, and 1,3-dicarbonyl compounds in the presence of a catalytic amount of Au NPs/silica-chitosan in water in excellent yields. Au NPs/silica-chitosan can be recovered easily and reused without any significant loss of the catalytic activity. 4H-pyran derivatives were synthesized using Au NPs/silica-chitosan as catalyst in three component reaction of isatins/aldehydes, active methylene, and 1,3-dicarbonyl compounds in water. Au NPs/Silica-Chitosan was prepared by reaction of aqueous solution of HAuCl4 (1 wt.%) and solution chitosan in deionized water and acetic acid with tetraethyl ortho silicate (TEOS) at 100ºC for 24 h. Gold nanoparticle functionalized mesoporous silica-chitosan was prepared and its catalytic activity was investigated for forming 4H-pyran derivatives. In this study, active methylene and 1,3-dicarbonyl compounds reacted with various isatins and aldehydes which afforded the corresponding spirooxindoles with 88-98% yields. This method includes the environmentally friendly reaction conditions, short reaction time, simple work-up, excellent yield, broad scope of usable substrates, recovery and reusability of heterogeneous catalyst.