Synthesis of 7-hydroxy-6H-benzo[c]chromen-6-ones based on a ‘[3+3] cyclization/domino retro-Michael–aldol–lactonization’ strategy

Synthetic versatility of 2-substituted-6-methyl 2,3-dihydropyridinones in the synthesis of polyfunctional piperidine-based compounds and related β amino acid derivatives

Chiral 2-substituted-6-methyl 2,3-dihydropyidinones 9, which can be facilely obtained from an asymmetric vinylogous Mannich reaction (VMR) with 1,3-bis-trimethysily enol ether, were used as versatile intermediates in constructing chiral polyfunctional piperidine-based compounds. The 6-methyl group of such compounds can be conveniently functionalized via alkylation and acylation reactions to provide efficient entries to the synthesis of a variety of chiral multi-substituted piperidine-based compounds. Further elaboration of the corresponding intermediates also provided access to polyfunctional indolizidine-based compounds. These methods were showcased in an asymmetric synthesis of 2,6-di-substituted piperidine compound 13, reported as the key intermediate in the synthesis of (+)-calvine and a natural alkaloid (-)-indolizidine 209D. Furthermore, selective C5 iodination of compound 9 enabled the installation of additional functional groups at this position. Finally, we demonstrated that the oxidative cleavage of 2-substituted-6-methyl-2,3-dihydropyidinones is a practical and efficient method for the enantioselective synthesis of β-amino acids, which can undergo further intra-molecular cyclization to give the corresponding chiral four-membered β-lactam derivatives.

Syntheses of benzo[c]coumarin carboxylic acids and fluorescence properties in the solid state

7-Hydroxy-3-methoxy-6-oxo-6H-benzo[c]- chromene-8-carboxylic acid (3a), 3,7-dihydroxy-6-oxo-6H- benzo[c]chromene-8-carboxylic acid (3b), 1,7-dihydroxy-6-oxo-6H-benzo[c]chromene-8-carboxylic acid (3c) and 2-bromo-7-hydroxy-6-oxo-6H-benzo[c]chromene-8-carboxylic acid (3d) were synthesized and characterized by the method of single crystal X-ray diffraction. Owing to bigger conjugated system and various H-bonds in 7-hydroxy-6-oxo-6H-benzo[c]chromene-8-carboxylic skeleton, 3a–3c have excellent fluorescence in ethanol solution and the solid state. The synthons involved in each crystal are identified, and the fluorescence emission differences leading to molecular recognition are determined.

One-pot synthesis of functionalized benzo[c]coumarins and their precursors via the reaction of 2-(polyfluoroalkyl)chromones with 4-alkyl-3-cyanocoumarins

2-(Polyfluoroalkyl)chromones react with 4-alkyl-3-cyanocoumarins in dichloromethane in the presence of triethylamine to give a wide variety of functionalized benzo[c]coumarin derivatives in good yields.

Building polyfunctional piperidines: a stereoselective strategy of a three-component Mannich reaction inspired by biosynthesis and applications in the synthesis of natural alkaloids (+)-241D; (−)-241D; isosolenopsin A and (−)-epimyrtine

A stereoselective strategy for building polyfunctional piperidines by a three-component Mannich reaction and applications in the stereoselective synthesis of natural alkaloids.