Cellulose-supported hyper-crosslinked l-tryptophan as an efficient chiral catalyst support for improved catalytic performance

Abstract

In this work, L-tryptophan was hyper-crosslinked on cellulose and several other matrices (such as silica gel and polystyrene) via a Friedel–Crafts alkylation reaction to produce a series of chiral hyper-crosslinked catalyst supports (HCP-Mt-(L)Trp). Transition metal catalysts (M) were then fixed on the resulting supports via coordination with the amino acid residues, generating heterogeneous chiral catalysts (HCP-Mt-(L)Trp-M). All the catalysts successfully catalyzed the asymmetric Henry reaction, and the influence of the matrix on the catalytic performance was investigated. It is found that the choice of matrix significantly affects the catalytic performance; matrices supported on cellulose show the best performance, and they led to good yields and enantioselectivity at both low and high temperatures (enantiomeric excesses up to 99% and yields of >80%). The catalysts can be readily recycled via filtration and show good recyclability. This work provides an effective strategy for the synthesis of highly efficient asymmetric catalysts with both high selectivity and ease of preparation.