Reactions of phosphite esters and trisdialkylaminophosphines with 5‐substituted 1,3,4‐thiadiazol derivatives

5‐{(1E)‐(4‐methoxyphenyl)methylene]amino}‐1,3,4‐thiadiazole‐2‐thiol ( 1a ) reacts with trialkyl phosphites ( 2a–c ) to give the respective dialkyl phosphonate adducts ( 4a–c ). On the other hand, the reactions of trisdialkylaminophosphines ( 3a,b ) with 1a , 5‐{(1E)‐(4‐phenyl)methylene]amino}‐1,3,4‐thiadiazole‐2‐thiol ( 1b ) yield the corresponding open dipolar structures 6a–c . In the case of the reaction of triethyl phosphite ( 2a ) with 1b , both the dialkyl phosphonate adduct ( 7 ) and the dipolar product ( 8a ) are obtained. Moreover, triisopropyl phosphite ( 2c ) reacts with 1b to give both the S‐alkyl and the N‐alkyl phosphonate adducts ( 9a,b ), respectively. Mechanisms are proposed to explain the formation of the new products, and their structures were confirmed on the basis of elemental analysis and spectral studies. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:594–601, 2001