Forty Years of Heterocyclic Sulfur Chemistry

Beginning in 1947, our studies were initially mainly devoted to 1,2-dithiole-3-thiones and their derivatives but were rapidly extended to other types of heterocyclic sulfur compounds: thiopyrans, thiocoumarins, thiochromones, thioisocoumarins, 3,1-benzothiazine-4-thiones and 1,2-dihydro-3,1-benzothiazine-4-thiones. In the course of these researches, some other heterocycles were also obtained such as thiophenes and 2,1-benzisothiazoles. Starting in 1958, considerable attention was given to compounds in which partial bonding exists between sulfur and oxygen or between several sulfur atoms. At first our work mainly concerned α-(1,2-dithiol-3-ylidene) ketones and 1,6,6aλ 4 -trithiapentalenes but later dealt also with other heterocyclic compounds, containing for instance thiopyran rings, and with extended structures in which the partial bonding affects four or five sulfur atoms in line. Last, in the course of our studies on heterocycles containing nitrogen and sulfur, we discovered new phosphorus-containing heterocyclic compounds, the 1,2-dihydro-3,1,2λ 5 -benzothiazaphosphinine-2,4-dithiones.