Heteroatom Chemistry Volume 12, Number 7, 2001 Reactions of Phosphite Esters and Trisdialkylaminophosphines With 5-Substituted 1,3,4-Thiadiazol Derivatives Mona H. N. Arsanious, 1 Yevette A. Issac, 2 and Leila S. Boulos 1 1 National Research Centre, Dokki, Cairo, Egypt 2 Faculty of Science, Benha University, Benha, Egypt Received 13 December 2000; revised 4 May 2001 ABSTRACT: 5-{[(1E)-(4-methoxyphenyl)methylene] amino}-1,3,4-thiadiazole-2-thiol (1a) reacts with tri- alkyl 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 phos- phonate 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 phos- phonate adducts (9a,b), respectively. Mechanisms are proposed to explain the formation of the new prod- ucts, and their structures were confirmed on the basis of elemental analysis and spectral studies. C  2001 John Wiley & Sons, Inc. Heteroatom Chem 12:594–601, 2001 INTRODUCTION The antibacterial, fungicidal, and pharmacological characteristics [1–3] inherent in substituted 1,3,4- oxa- and thiadiazole derivatives enhanced the synthesis of new compounds incorporating such important nuclei that may possibly lead to further biological activity. Our continuing interest in organo- phosphorus syntheses [4–8] led us to investigate Correspondence to: Leila S. Boulos; e-mail: monaser@link.net. c  2001 John Wiley & Sons, Inc. the reactivity of 5-{[(1 E)-(4-methoxyphenyl)methy- lene]amino}-1,3,4-thiadiazole-2-thiol (1a) and 5- { [ (1 E)-(4-phenyl) methylene] amino}-1,3,4-thiadia- zole-2-thiol (1b) toward trialkyl phosphites (2a–c), and trisdialkylaminophosphines (3a,b) (Scheme 1). RESULTS AND DISCUSSION We have found that the reaction of 1a (pre- pared by the reaction of 2-amino-5-mercapto- 1,3,4-thiadiazole with 4-methoxybenzaldehyde) with 2 mole equivalents of triethyl phosphite (2a) in dry toluene proceeds at reflux temperature to give the dialkyl phosphonate adduct (4a) in 86% yield (Scheme 2). Structure elucidation of the diethyl phosphonate adduct (4a) is based on the follow- ing evidence: (i) Compound 4a exhibits δ =+21.19 in its 31 P NMR spectrum which clearly indicates a phosphonate structure [9,10]. (ii) The IR spectrum of 4a shows strong absorption bands at 1248 cm −1 (P O), 1023 cm −1 (P O C 2 H 5 ) [11], and at 3453 cm −1 (NH). Moreover, its IR spectrum lacks the thiol (SH) absorption band appearing in the spectrum of (1a) at 2800 cm −1 . The 1 H and 13 C NMR spectra also furnish strong evidence in support of the phospho- nate structure 4a (cf. Experimental). The mass spec- trum of 4a yielded a prominent ion peak for M + at m/z 417. Compound 4a can also be obtained by the reac- tion of the alkylated product (5) (prepared from 1a and ethyl iodide) with excess triethyl phosphite (2a) in boiling toluene (cf. Scheme 2, Experimental). 594