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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.

Abstract:The present account summarizes the author's studies to elucidate the mechanisms of the recently reported rearrangements resulting from inter-and/or intramolecular reactions of 2-imino-2H-chromene-3-carboxamides with different dinucleophiles.

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Using o-phenylenediamines, o-aminophenoi or o-aminothiophenol, 2-iminocoumarin-3-carboxamide can be recyclized to the corresponding 3-(1H-benzimidazol-2-yl), 3-0aenzoxazol-2-yl), or 3-(benzothiazol-2-yl) coumarins. An alternative synthesis has been carried out and an analytical comparison of the synthetic routes made.In previous publications we have described recyclization processes for 2-iminocoumarin-3-carboxamides which can give N. -benzoylamidrazones of coumarin-3-carboxylic acids, 3-(1,3,4-oxadi-, thiadi-, and triazol-2-yl)coumarins [1], and 3-(1,1-dioxo-2H-benzo-l,2,4-thiadiazin-3-yl)coumarins [2]. Continuing this investigation we have studied the reaction of 2-iminocoumarin-3-carboxamides with o-phenylenediamines, o-aminophenol, and o-aminothiophenol.It was found that refluxing 2-iminocoumarins with o-phenylenediamines, o-aminophenol, or o-aminothiophenol in butan-l-ol gives, respectively, 3-(1H-benzimidazol-2-yl), 3-(benzoxazol-2-yl), or 3-(benzothiazol-2-yl)coumarins IIIa-j (see Scheme 1).We had previously shown that reaction of 2-iminocoumarins with primary amines gave high yields of 2-N-Rsubstituted iminocoumarins [3]. In the present case it might be expected that 2-(N-[o-amino(hydroxy, mercapto)phenyl]imino)coumarins A would be formed. However, as shown by spectroscopic investigation (Tables 1 and 2), this reaction does not stop at the stage of formation of the 2-N-R-iminocoumarins (A) but goes further via a recyclization step to give the 3-heterylcoumarins IIIa-j. In the PMR spectra of the products IIIa-j ( Table 2) the signals of the non equivalent NH2 protons of the carbamide group at 8.20-8.40 and 7.45-7.65 ppm have disappeared and, in the case of the benzimidazole derivatives IIIa-e, a singlet for the NH proton appears at 12.31-12.60 ppm appears. A singlet signal for the proton at position 4 of the coumarin is seen at 9.00-9.70 ppm. The IR spectra of these compounds (Table 1) show an intense lactone C=O stretching band at 1726-1674 cm -1. Compounds IIIa-e show a broad NH band at 3354-3262 cm -1. In addition, 3-(1H-benzimidazol-2-yl), 3-(benzoxazol-2-yl), and 3-(benozthiazol-2-yl) coumarins IIIa-j have UV spectra which are typical of 3-heterylcoumarins [1] and have marked fluorescence properties.The reaction course indicated can be explained via formation in the first stage of the 2-N-R-iminocoumarin A (which is subsequently recyclized through attack of a second nucleophilic center (OH, NH2, SH) at the carbon atom of the C=N bond) followed by opening of the "iminolactone" ring and then closing of the coumarin ring.During the reaction of 2-iminocoumarin-3-carboxamide with o-phenylenediamine there is also formed in 5-10% yield 2-(2-hydroxyphenyl)benzimidazole which was isolated from the basic recyclization product via chromatography of the reaction medium and was identified by a mass spectrometric method. The formation of the same product was also noted when fusing the unsubstituted coumarin with o-phenylenediamine [4]. *For Communication 2 see [2].Ukraine Pharmaceutical Academy, Khar'kov 310002.