Carbon–carbon bond formation by intramolecular 1,4-dipolar cycloaddition: heterocyclic betaines generated in situ from amides and N-substituted amides

Abstract

Reaction of benzamides and N-substituted benzamides with appropriate o-alkenyl and -alkynyl side-chains and (chlorocarbony1)phenyl ketene gives transient anhydro-I ,3-oxazinium hydroxides which readily undergo intramolecular 1,4-dipolar cycloaddition; loss of C 0 2 from these 1 : 1 -cycloadducts, isolable with N-su bstituted systems and alkenyl side-chains, gives chromeno[4,3-b]pyridin-2-ones.Intramolecular 1,3-dipolar cycloadditions have become an established method for heterocycle construction;' intramolecular 1 ,bdipolar cycloadditions have received less attention , with difficulties encountered in generating the 174-dipole being avoided by incorporating the 1,4-dipole in a heterocyclic betaine.2 We now describe an approach in which the heteroaromatic betaine is generated in situ and the use of tautomerism in this is exploited.t Author to whom enquiries about X-ray crystallographic analysis shoud be directed.

A Convenient One-Pot Synthesis of Pyrano[3,2-c]quinolin-2,5(6H)-dione and 2H,5H-Pyrano[3,2-c]chromene-2,5-dione Derivatives

“…Chlorocarbonyl ketenes have been found to be a very effective 1,3-bielectrophiles reacting with a variety of nucleophiles under rather mild experimental conditions, and have been used mainly for the synthesis of five-and sixmembered heterocyclic compounds. 11,12 In continuing our interest in the synthesis of heterocyclic compounds we wish to report in this paper a one-pot synthesis of pyrano[3,2-c]quinolin-2,5(6H)-dione and 2H,5H-pyrano[3,2-c]chromene-2,5-dione derivatives using the reaction of 4-hydroxyquinolin-2(1H)-ones and 4-hydroxy-2H-chromene-2-one with chlorocarbonyl ketenes and diethyl phenylmalonate in good to excellent yields.…”

The condensation of (chlorocarbonyl)phenyl ketene with 1,3-dinucleophiles. I. Synthesis of 4-hydroxy-2-(1H)-pyridinones and mesoionic 1,3-oxazinium olates

“…18,19 We now report the preparation of a series of 1,3-oxazinium olates from the reaction of N-monosubsitituted 4-methoxy or 2,4-dimethoxy benzamide derivatives with (chlorocarbonyl)phenyl ketene without the use of triethylamine. The present protocol offers several advantages including high yields, operational simplicity and clean reaction conditions (Scheme 3).…”

“…3 These ketenes have been found to be very effective 1,3-dielectrophilic reagents and react with a wide variety of nucleophiles under mild experimental conditions, and have been used mainly for the synthesis of five-and six-membered heterocycles functionalized with oxo and hydroxyl groups in the 1,3-positions. 4,5 Structures containing the 2(1H)-pyridinone (2-pyridone) skeleton are rapidly gaining importance in synthetic and natural product chemistry. Compounds incorporating this nucleus are quite versatile as synthetic intermediates.…”

Studies on condensation of chlorocarbonyl phenyl ketene with N-unsubstituted amides: synthesis of some new 1,3-oxazin-6-ones

“…They were predominantly used in the synthesis of five and six membered heterocycles functionalized with hydroxy groups in 1,3 positions. 5, 6 In continuation of our study on the reactions of chlorocarbonyl ketenes with 1,2 dinucleophiles (oximes 7 and hydrazones 8 ) and 1,3 dinucleophiles (1,3 dicarbonyl compounds, 9,10 thio amides, and amides 11 ), we studied a facile condensation of chlorocarbonyl phenyl ketene with N unsubstitut ed amides and synthesized some new 1,3 oxazine deriva tives (Scheme 3).…”