Reactions of diethyl 3-methylbuta-1,2-dienylphosphonate with 2-aminobenzothiazole

Abstract

A reaction of diethyl 3 methylbuta 1,2 dienylphosphonate with 2 aminobenzothiazole afforded 1 diethoxyphosphoryl 2 (2 imino 2,3 dihydrobenzothiazol 3 yl) 3 methylbut 2 ene.Key words: buta 1,2 dienylphosphonate, 2 aminobenzothiazole, β amino alkenyl phosphonates.In recent years, aminoalkyl(alkenyl)phosphonates have attracted much attention not only as compounds with a broad spectrum of biological activities but also as complexones, emulsifiers, and membrane carriers. 1-4 Reactions of primary and secondary aliphatic amines with unsaturated derivatives of four coordinate phosphorus acids are thoroughly studied and used to obtain β amino alkyl(alkenyl)phosphonates in good yields. 2,5,6 However, only a few studies have been devoted to the synthesis of phosphonates functionalized in the β position with nitro gen containing heterocyclic fragments. 2,7,8We investigated a reaction of diethyl 3 methylbuta 1,2 dienylphosphonate 1 with 2 aminobenzothiazole 2. For this reaction, two pathways are possible: the central C atom of the allene system could be attacked by the ring N atom (adduct 3) or the N atom of the exocyclic amino group (adduct 4, Scheme 1).Heating of an equimolar mixture of the reagents gave a crystalline product. Its 31 P NMR spectrum in solution shows a single signal at δ P 26.2. The 1 H NMR spectrum contains doublets for the protons of two methyl groups at the sp 2 hybridized C atom at δ 1.53 ( 5 J P,H = 5.8 Hz) and 1.94 ( 5 J P,H = 4.4 Hz). The spectrum shows a signal at δ 3.03 ( 2 J P,H = 20 Hz) for the protons of the α methylene group relative to the phosphoryl fragment. The signals for * Dedicated to the Corresponding Member of the Russian Acad emy of Sciences T. A. Mastryukova. Scheme 1