Facile Synthesis of Thiazole, Thiazine and Isoindole Derivatives via EDA Approach and Conventional Methods

The reactivity of N-amidinothiourea (1) as an electron donor towards several electron-accepting functional groups via electron-donor-acceptor (EDA) interaction has been studied. Thus on treatment of 1 with either 1,1,2,2-tetracyanoethylene (TCNE, 2), 2,3-dicyano-1,4-naphthoquinone (DCNQ, 4), 2,3,5,6-tetrabromo-1,4-benzoquinone (BHL-p, 6), 2,3-dichloro-1,4-naphthoquinone (DCHNQ, 8), 2,3,5,6-tetrachloro-1,4-benzoquinone (CHL-p, 13), 2,3-dicyano-5,6-dichloro-1,4benzoquinone (DDQ, 15), 2-dicyanomethyleneindan-1,3-dione (CNIND, 17), 2-(2-oxoindolin-3ylidene)malononitrile (19), and/or dimethyl acetylenedicarboxylate (DMAD, 21), the reaction proceeds to give thiazole and thiazine derivatives, respectively. However, isoindole derivatives 24 and 26 were formed on heating of 1 with either tetrabromophthalic anhydride and/or o-phthalaldehyde, respectively. The products were fully characterized according to their spectral data. The mechanisms of formation of the products have been rationalized.