John Louis Suschitzky

Synthesis of 2-substituted chromones, chromanones, and their thio analogues using organocopper reagents

Improved use of organocopper reagents provides a general route to unsymmetrical 2,2-dialkylchomanones and thiochromanones from chromones and thiochromones via a simple addition - oxidation - addition sequence

Transformation of 3-formylchromones into pyridines and pyrroles

Abstract Interaction of 3-formylchromones with ethyl aminoethanoate provides a novel route to pyridines and pyrroles.

Reactions of formylchromone derivatives. Part 5. Transformations of 3-formylchromones into pyrroles and pyridines

4-Oxo-4H-1-benzopyran-3-carbaldehyde (3-formylchromone)(1) was treated with various bi-functional nucleophiles. With ethyl aminoethanoate it gave a mixture of ethyl 4-(2-hydroxybenzoyl)-6-(4-oxo-4H-1-benzopyran-3-yl)pyridine-2-carboxylate (2) and ethyl 4-(2-hydroxybenzoyl)pyrrole-2-carboxylate (3) whereas with 2-aminoethanonitrile, only the pyridine, 2-cyano-4-(2-hydroxybenzoyl)-6-(4-oxo-4H-1-benzopyran-3-yl)pyridine (7) was obtained. Ethyl 2-aminopropanoate or ethyl 2-amino-2-phenylethanoate both gave the same pyrrole, 4-(2-hydroxybenzoyl)-2-(4-oxo-4H-l-benzopyran-3-yl)pyrrole (8). and N-methylethanoic acid yielded 3-(2-hydroxybenzoyl)-N-methyl-pyrrole (9). Corresponding products were usually obtained when various substituted 3-formylchromones were used in the reactions. Mechanistic pathways are proposed to account for all the products and the pyridine structure was confirmed by degradation.

Some reactions of carbenoids with chromone-2-carboxylic esters

Ethyl 5-hydroxy-4-oxo-8-propyl-4H-[1]benzopyran-2-carboxylate (3a) reacts with chloroacetone under basic conditions to yield (1α, 1aα, 7aα)- and (1β, 1aα, 7aα)-ethyl 1-acetyl-1,1a,7,7a-tetrahydro-6-hydroxy-7-oxo-3-propylbenzo[b]cyclopropa[e]pyran-1a-carboxylate (4a) and (5a), products of cyclo-propanation of the chromone 2,3-double bond, as well as ethyl 1,7-diacetyl-7, 7a-dihydro-5-propyl-6aH-cyclopropa[b]furo[4,3,2-de][1]benzopyran-6a-carboxylate (6a), representing a novel ring system. The corresponding tetrahydronaphthopyran (3b) gives analogous products (4b), (5b), and (6b). The thiochromone analogue of (3a), (8), gives only the furan annelated product ethyl 2-acetyl-6-propylthio-pyrano[4,3,2-cd]benzofuran-4-carboxylate (9) under similar conditions. The reaction of the chromone (3b) with dimethylsulphoxonium methylide to yield the isomeric naphthofuranones (16a) and (17a) is also described.

Comments on the electronic structure and reactivity of chromones

AB initio calculations of ground-state wavefunctions of chromones and thiochromones have been carried out and correlated with the observed reactivity of these molecules. Quantum mechanical electrostatic potentials correctly predict nucleophilic attack to occur preferentially at C-2 and C-4 in chromones and thiochromones respectively. Frontier-orbital considerations correctly predict the site selectivity of the photochemical cycloaddition to the pyrone double bond of chromone.