Synthesis and Stereochemistry of Some New Thiazolidines

Abstract

Variety of 3-substituted-5-(2-aryl-2-oxoethyl)-2- thioxo-4-oxo-1,3-thiazolidines (143) have been• synthesized by treating aroylacrylic acids with ammonium aryldithiocarbamates, then reacted with different reagents to produce many new fused and spiro heterocycles containing the thiazolidine ring system. Thus, thionation of 143a-e either with tetra­ phosphorous decasulphide or with Lawesson's reagent affords the respective 3-substituted-5-aryl-2,3-dihydro­ thieno[2,3-d] I ,3-thiazole-2-thiones (144a-e). However, thionation of 143f affords 3-(3-methylphenyl)-6-(4- ethy1phenyl)-2-thioxo-2,3-dihydrothiazolo[4,5-c]1,2-dithiin (145a). Compounds 143a,c,h react with aldehydes 153a-d in the presence of ammonium acetate in toluene to afford mixtures of the following compounds: 2,5-diaryl-3'­ substituted-2'-thioxo-4'-oxospiro[2,4-dihydropyrrole-3,5'­ thiazolidine] (154a-f and 155a-t), in good overall yields, and in varying proportions. Repeated recrystallization from proper solvents produces compoiLinds 154a,b,c,e,f and 155d, in a pure state. Bromine reacts with 154c in cold chloroform solution to afford a mixture of the 2,4-dione (156c), the 4-bromo­ deviations (157c and 158c) and the 4-bromo dione (159c). Compound 157c has the H-2 in the axial conformation, whereas, 158c has the H-2 in the equatorial position. Molecular Modelling Computer software program shows that 157c and 158c have the 2(R), 3(S), 3'(R,S)- and the 2(S), 3(R), 3'(R,S)- configurations, respectively: Similar treatment of 154a provides a mixture of 158a and 159a, in the ratio of 3:2 respectively, where 155d affords a mixture of 160d and the respective 2,4-dione