Regio- and π-Facial Selective Cycloadditions Involving 2-Phenyl-4-dimethylamino-1-thia-3-azabuta-1,3-diene and Allenic Esters: An Efficient Route to Novel 6-Alkylidene-6H-2-phenyl-5-ethoxycarbonyl-1,3-thiazines

Abstract

2-Phenyl-4-dimethylamino-1-thia-3-azabuta-1,3-diene (4) undergoes regio- and stereoselective [4+2] cycloadditions with allenic esters on refluxing in CH₂Cl₂-benzene and the initially formed cycloadducts 6 furnish, after elimination of dimethylamine, novel (E/Z)-6-alkylidene-6H-2-phenyl-5-ethoxycarbonyl-1,3-thiazines 7 and 8 in high yields. In the case of reaction with ethyl 2-methylbuta-2,3-dienoate, the adduct 6e has been isolated in very high yields.

Key words

1-thia-3-azabuta-1,3-diene - allenic esters - cycloadditions - 1,3-thiazines - hetero Diels-Alder reaction

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