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1860-5397-2-4 - Synthesis of phosphorothioates using...

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Page 1 of (page number not for citation purposes) 5 Synthesis of phosphorothioates using thiophosphate salts Babak Kaboudin * and Fatemeh Farjadian Full Research Paper Open Access Address: Department of Chemsitry, Institute for Advanced Studies in Basic Sciences, Gava Zang, Zanjan 45195-1159, Iran Email: Babak Kaboudin * - [email protected]; Fatemeh Farjadian - [email protected] * Corresponding author Beilstein Journal of Organic Chemistry 2006 , 2, No. 4. doi:10.1186/1860-5397-2-4 Received: 10 December 2005 Accepted: 16 March 2006 Published: 16 March 2006 © 2006 Kaboudin and Farjadian; licensee Beilstein-Institut. License and terms: see end of document. Abstract Reactions of O,O '-dialkyl thiophosphoric acids with alkyl halides, in the presence of a base, provide a direct synthetic route to phos- phorothioates via O,O '-dialkyl thiophosphate anion formation. Studies on the reaction of ambident nucleophile ammonium O,O '- diethyl thiophosphate with benzyl halides and tosylate in different solvents show that only S -alkylation is obtained. Reaction of this ambident nucleophile with benzoyl chloride (a hard electrophile), gave the O -acylation product. A simple, efficient, and general method has been developed for the synthesis of phosphorothioates through a one-pot reaction of alkyl halides with the mixture of diethyl phosphite in the presence of triethylamine/sulfur/and acidic alumina under solvent-free conditions using microwave irradi- ation. Introduction Organophosphorus compounds have found a wide range of application in the areas of industrial, agricultural, and medi- cinal chemistry owing to their biological and physical proper- ties as well as their utility as synthetic intermediates. [1] The synthesis of phosphate esters is an important objective in organic synthesis, since they have found use in the preparation of biologically active molecules, and also versatile intermediate in synthesis of amides and esters. [2-4] Among the phosphate esters, phosphorothioate derivatives are of interest as effective pesticides. [5-8] In recent years a number of phosphorothioates have been introduced as potential chemotherapeutic agent. [9-12] Despite their wide range of pharmacological activity, industrial and synthetic applications, the synthesis of phos- phorothioates has received little attention. The following methods, not generally applicable, have been reported in the literature: (i) reaction of dialkyl phosphites with sulfenyl chlor- ides,[13] sulfenyl cyanides,[14] thiosulfonates,[15,16] disulf- ides,[17] and sulfur, [18-21] (ii) condensation of phosphorchlor- idate with thiols [22-26] and (iii) redox-type reactions of phos- phorus triesters with thiols in the presence of tellurium (IV) chloride. [27,28] However, all of these methods have problems, including drastic reaction conditions and also some severe side reactions. Surface-mediated solid phase reactions are of growing interest [29-35] because of their ease of set-up, work- up, mild reaction conditions, rate of the reaction, selectivity, high yields, lack of solvent and the low cost of the reactions in
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Beilstein Journal of Organic Chemistry 2006 , 2, No. 4.
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