Synthesis of N,O-Type Inherently Chiral Calix[4]arenes Substituted on the Lower Rim and their Organocatalysis Properties

Abstract

This work presented the first study of organocatalytic behaviors of inherently chiral calix [4] arenes substituted at the lower rim. A pair of N,O-type enantiomers based on inherently chiral calix [4]arenes substituted at the lower rim were readily synthesized and applied to catalyze Henry reaction between aromatic aldehydes and nitromethane. Their organocatalytic reaction can afford the desired products in excellent yields (up to 99%) but poor enantioselectivities (up to 7.5% ee).

Mononitration of a Calix[4]arene Methylene Bridge: Synthesis and Preliminary Catalysis Performances of Bridging Chiral p-tert-Butylcalix[4]arenes with a Monoamino Bridge Substituent in a 1,3-Alternate Conformation

“…The crude residue was loaded directly onto a silica gel column and purified by flash chromatography. The absolute configurations of all products were determined by comparing the retention time from HPLC data on the products with those in the literature data …”

Recent applications of chiral calixarenes in asymmetric catalysis

“…But their use in asymmetric organocatalysis hasn’t been reported. To explore the organocatalytic behaviors of inherently chiral calix[4]arenes modified at the lower rim, Li et al reported the synthesis of N,O -type enantiomers based on inherently chiral calix[4]arene ( Scheme 5 ) [ 41 ]. The synthetic sequence starts from a pair of optically pure inherently chiral calix[4]arene diastereomers 16a/16b and contains four steps to lead 20a/20b as a pair of enantiomers.…”

α‐Methylbenzylamine Functionalized Crown‐Ether‐Appended Calix[4]arene Phase Transfer Catalyst for Enantioselective Henry Reaction

“…[16] However, calixarene-derived PTCs for asymmetric Henry reaction is virtually absent in the literature. To the best of our knowledge, the only reported examples pertaining to calix [4]arene functionalized organocatalysts for Henry reaction are reported with poor enantioselectivities by Ma [17] (7.5 % ee) and Li [18] (22.3 % ee). Hence the design of effective PTCs for Henry reaction with high enantioselectivity under mild conditions remains the sine qua non to date.…”