Sulfur transfer reagents in heterocyclic

Thionyl chloride (SOCl2) is the most versatile of all sulfur transfer reagents in heterocyclic synthesis. The sulfur-oxygen bond renders the sulfur atom more electrophilic the possibility of ready removal by elimination of the oxygen atom allows easy aromatization of many of the initially formed sulfur heterocycles. Two general reviews of the chemistry of thionyl chloride are available.53 Both cover the literature up to about 1970. 

Recent Advances in the Chemistry of Benzisothiazoles and Other Polycyclic Isothiazoles, 38, 105 Sulfur Transfer Reagents in Heterocyclic Synthesis, 30, 47. 

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