1.3.4- Thiadiazolines, fragmentations

The principal fragmentation of 1,3,4-thiadiazoles in the mass spectrometer is loss of a nitrile group as shown in Scheme 1. In the presence of a methylthio substituent, the major process is loss of SH and fragmentation at the heterocyclic sulfur atom (Scheme 2). In 1,3,4-thiadiazolines the major pathway is loss of PhS (Scheme 3) while 1,3,4-thiadiazolidinediones decompose by fragmentation of the ring . 

Dipolar cycloreversion was found for several, mainly the heteroatom-rich, compounds such as pentazole (48), tetrazoles (38,46,47,48), tetrazo-lines (43), tetrazolinones (44) and -thiones (45), 1,3,4-thiadiazolines (39), 1,3,4-oxadiazolidines (42), 13,4-oxathiazolinone (40), and 1,2,3-thiadiazole (49). When the compound has an exocyclic double bond, this ring fragmentation produces two compounds with cumulated double bonds. 

The fragmentation of 2-phenyl-1,3,4-thiadiazolin-5-one and -5-thione begins with the breaking of the C—N bond followed by the ejection of the S=C=Y molecule (Y = O or S). The major part of AH°R is associated with the stabilization of the neutral fragment (810MS29). 

The mass spectra of a series of 3-amino-4-aryl-5-aryl(or alkyl)imino-A2-1,2,4-thiadiazolines (366) have been interpreted in terms of fragmentation patterns, that are the result of fission of the molecules by routes a-c.257 (see also Ref. 49). In an extension of this study to variously substituted 3,5-... 

Nitrosamines derived from 5-amino-1,2,4-thiadiazoles are readily accessible stable compounds.3 Thermolysis of the substituted 5-nitrosoimino-1,2,4-thiadiazolines (48574 and 486383) produces the corresponding 5-ketones (487, 488) with evolution of nitrogen almost quantitatively. Their photolysis, involving n- n excitation, proceeds less uniformly. Irradiation of 486 in various solvents yields, as primary products, Hector s base (14b) and phenyl-cyanamide subsequent changes produce their 1 1-adduct, as well as 3,5-dianilino-l,2,4-thiadiazole, phenylurea, and other compounds, all in variable moderate yield. The photolytic fragmentation is more complex than that of comparable heterocyclic nitrosimines.384... 

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