Furan 2-mercapto-, tautomers

Mercapto derivatives of furan, thiophene, selenophene (77ACS(B)198) and pyrrole (72AJC985) all exist predominantly in the thiol form. 2-Mercaptobenzothiophene is also a thiol (70JCS(C)243i) whereas 2-mercaptoindole is mainly indoline-2-thione (89) (69CPB550). The finely balanced nature of this system is indicated by the fact that a 3-aryl, but not a 3-alkyl, substituent will stabilize the 2-thiol form, whereas for 3-aryl-fV-methyl derivatives the 2-thione tautomer is preferred (71CC836). 

The known 3-mercapto derivatives of furan, thiophene, selenophene (77ACS(B)198), ben-zothiophene (70JCS(Q243i) and indole (69TL4465) all exist as the 3-thiol tautomers. 

Proton n.m.r. and i.r. studies on 2-mercapto-5-methyl- and 2,5-dimethyl-3-mercapto-furan, -thiophen, and -selenophen indicate the presence of mainly the thiol tautomers.Carbon-13 n.m.r. has been used to distinguish thione and selenone tautomers in appropriately substituted 1,3,4-thiadiazoles and -selenadiazoles, and tetrazole derivatives. N.m.r., i.r., and u.v. studies indicate that 4-aminoisothiazole exists as the amino- and not the imino-tautomer. ... 

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See also in sourсe #XX -- [ ]

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