An efficient and direct synthesis of 1-thia-5-azaspiro[5.5]undec-2-ene is described, and the basecatalyzed recyclization of this compound was studied. The products have been characterized by elemental analyses, and IR, MS, 1 H NMR, and 13 C NMR spectroscopy.

An efficient and direct procedure for the synthesis of 2,2`-(1,4-phenylene)bis-3,4-dihydro-2H-1,3- thiazin-4-one derivatives is described. Oxidation of the latter and their base-catalyzed recyclization has been studied. The products were characterized by elemental analyses, and IR, 1H NMR, and 13C NMR spectra.

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An efficient and direct procedure for the synthesis of 1-thia-5,9-diaza-spiro[5.5]undec-2-ene has been described. The base-catalyzed recyclization of the latter has been studied. The structures of the products were proved by elemental analyses, IR, MS, 1 H-and 13 C-NMR spectroscopy.

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