Chitosan as a sustainable heterogeneous catalyst for the preparation of functionalized α-diazo carbonyl compounds

Abstract

The food industry generates vast amounts of waste and one of the most abundant is the biopolymer chitin, which is the main constituent of crustacean shells and insect exoskeletons. The alkaline deacetylation of the N-acetyl-d-glucosamino units of chitin leads to chitosan, a stable, inexpensive, non-toxic, biocompatible, and biodegradable material of basic properties due to the presence of free amino groups. In the present study, we report the catalytic activity of commercially available chitosan as a sustainable heterogeneous catalyst for the preparation of α-diazo carbonyl compounds through the diazo transfer reaction to active methylene compounds using a sulfonyl azide as the diazo transfer reagent. Thus, 17 α-diazo carbonyl compounds were readily prepared under mild conditions in 50–92% yield after a simple work-up consisting of vacuum filtration to separate the insoluble catalyst and the sulfonamide byproduct. This procedure was also adapted to aqueous medium, making the process more environmentally benign. The recovery and recyclability of the biocatalyst were also addressed, with the catalytic activity being slightly reduced after four reuses depending on the substrate used. The synthetic potential of diazo carbonyl compounds was further demonstrated through the rhodium-catalyzed O–H insertion reactions.

Keywords

• Chitosan
• α-diazo carbonyl compounds
• Heterogeneous catalysis
• Green chemistry