Peculiarities of 2-amino-3-R-4-aryl-4H-pyranes multicomponent synthesis derived from 1H-2,1-benzothiazin-4(3H)-one 2,2-dioxide

Abstract

The new 2-amino-3-R-4-aryl-6-ethyl-4,6-dihydropyrano[3,2-c][2,1]benzothiazine 5,5-dioxides were synthesized via three-component interaction of 1H-2,1-benzothiazin-4(3H)-one 2,2-dioxide with arylcarbaldehydes and active methylene nitriles. Depending on the nature of an active methylene nitrile and an arylcarbaldehyde this interaction can lead either to the target 2-amino-4H-pyrans or to the stable triethylammonium salts of bis(1H-2,1-benzothiazin-4(3H)-one 2,2-dioxides) (bis-adducts). The latter is a completely new product of such interaction. The structure of the bis-adduct was confirmed by single crystal X-ray diffraction. Actually, the formation of stable triethylammonium salts (as the process competitive with the 2-amino-4H-pyrans formation) appeared to be reversible and their interaction with active methylene nitriles led to the formation of 2-amino-4H-pyrans. The extended and adjusted mechanism of the three-component interaction, that includes the bis-adducts formation stage, was proposed. Taking into account the peculiarities of the mechanism, we were capable to control the reaction selectivity.