Azoles and azines: CXXVIII. Reaction of 2-aryl-4-hydroxy-6H-1,3-thiazin-6-ones with 6-bromo-4-oxo-4H-chromene-3-carbaldehyde

Abstract

We previously studied reactions of 2-aryl-4-hydroxy-6H-1,3-thiazin-6-ones with aliphatic and aromatic aldehydes [2]; in these studies, specific attention was given to reactions of such 1,3-thiazines with salicylaldehyde derivatives [3], taking into account possible closure of coumarin ring in the reactions with malonic acid derivatives, including cyclic ones (e.g., barbituric acid or 2-aryl-4-hydroxy-6H-1,3-thiazin-6-ones). Derivatives of 3-formylchromone also attract strong theoretical and practical interest due to the presence of double carbon–carbon bond (C 2 =C 3 ) activated by two carbonyl groups, which is capable of taking up nucleophilic reagents, including compounds with an activated methylene group [4]. Reactions of such chromones with polyhydroxypyrimidines (which can be regarded as cyclic analogs of malonic acid) give rise only to the corresponding ylidene derivatives as a result of condensation at the aldehyde group [5]. Reactions of 4-hydroxy-6H-1,3-thiazin-6-ones with substituted 3-formylchromones were not studied. We have found that 2-aryl-4-hydroxy-6H-1,3-thiazin6-ones Ia and Ib react with 6-bromo-4-oxo-4Hchromene-3-carbaldehyde (II) in polar aprotic solvents (such as DMSO or pyridine) to give 3,10-dioxo-Nthioaroyl-4,4a-dihydro-3H,10H-pyrano[4,3-b]chromene4-carboxamides VIIa and VIIb in 60–70% yield. It should be noted that the formation of such products is quite surprising, taking into account that the reaction of 3-formylchromone with barbituric acid leads to the formation of 5-(4-oxochromene-3-ylmethylidene)bar