Novel supramolecular organocatalysts of hydroxyprolinamide based on calix[4]arene scaffold for the enantioselective Biginelli reaction

Abstract

A series of novel supramolecular organocatalysts of hydroxyprolinamide based on the upper rim of calix[4]arene scaffold have been developed to catalyze enantioselective multi-component Biginelli reaction. Under the optimal conditions, the reactions occurred with moderate-to-excellent enantioselectivities (up to 98% ee). A plausible transition state constructed by the supramolecular interaction of hydrogen bond and cation- between catalysts and substrates has been proposed. supramolecular organocatalyst, calix[4]

Nanosized metal or silicon oxides and L‐proline or 4‐hydroxy‐L‐proline in stereoselective synthesis of a dihydropyrimidinethione podand

“…According to the literature data, 17,38–41 the stereoselective synthesis of both 5‐ethoxycarbonyl‐6‐methyl‐4‐phenyl‐3,4‐dihydropyrimidine‐2(1 H )‐one (classical Biginelli product) and corresponding thio analog lead to an enantiomeric excess of these products with the ( R )‐configuration in the presence of 4‐hydroxy‐ L ‐proline derivatives. Retention time (τ r ) of ( R )‐enantiomer of compound 6 was 8.17 min (Daicel Chirapak OD‐H, hexane/isopropanol = 80:20, flow rate 0.8 mL/min).…”

Recent applications of chiral calixarenes in asymmetric catalysis

“…The catalysts 69f–j ( Fig. 8 ) were successfully applied to the enantioselective multicomponent Biginelli reaction of benzaldehyde, ethyl acetoacetate and urea [ 68 ]. The results show that all five chiral calix[4]arene catalysts promote the formation of the dihydropyrimidine product with different extents in terms of chemical yield and enantioselectivity.…”

Enantioselective Organocatalyzed Transformations of β-Ketoesters

“…The organocatalyst backbone has been varied from commonly used alkaloid 18 , proline ( 98 , 99 , 100, and 102 ) and hydrocarbon scaffolds ( 97 and 104 ) to include calix[4]­arenes ( 103 ), carbohydrates ( 101 , ), and a sulphonimide 105 (Scheme ). − ,,− Early attempts focused on the use of chiral secondary amine organocatalysts, while chiral primary amine derived catalysts were being developed. Comparison of the enantioselectivity of the DHPM adducts when using secondary amine organocatalysts proved to be somewhat inferior compared with many of those obtained using primary aminocatalysts.…”