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1,3oxathiolan-5-one. water, and extracted with ether; the extract was washed with water, dried with anhydrous sodium sulfate and filtered, and the filtrate was distilled. Compound 2a (48 g, 80%) was obtained; bp 78-80°C (12 torr). 1 H NMR spectrum, δ, ppm (J, Hz); 1.31 (3H, t, 3 J HH = 7.2, OCH 2 CH 3 ); 3.52 (1H, d, 2 J HH = 15.9, AB, SCH 2 ); 3.61 (1H, d, 2 J HH = 15.9, AB, SCH 2 ); 4.24 (2H, q, 3 J HH = 7.2, OCHH 2 CH 3 ); 5.51 (1H, q, 3 J HF = 6.6, CF 3 CH). 19 F NMR spectrum, δ, ppm (J, Hz): -72.80 (3F, d, 3 J HF = 6.6, CF 3 CH). Found, %: Cl 15.33; S 13.39. C 6 H 8 ClF 3 O 2 S. Calculated, %: Cl 14.98; S 13.55.[2-(1-Chloro-2,2,2-trifluoroethyl)thio]thio]propionic Acid Methyl Ester (2b) was obtained as for compound 2a, as a mixture of diastereoisomers (1:1). Yield 72%; bp 80-82°C (12 torr). 1 H NMR spectrum, δ, ppm (J, Hz): 1.54 (3H, d, 3 J HH = 7.3, CH 3 CH) and 1.57 (3H, d, 3 J HH = 7.3, CH 3 CH): 3.75 (1H, q, 3 J HH = 7.3, CHCH 3 ) and 3.78 (1H, q, 3 J HH =7.3, CHCH 3 ); 3.79 (3H, s, OCH 3 ) and 3.793 (3H, s, OCH 3 ); 5.47 (1H, q, 3 J HF = 6.7, CHCF 3 ) and 5.58 (1H, q, 3 J HF = 6.7, CHCF 3 ). 19 F NMR spectrum, δ, ppm (J, Hz): -72.86 (3F, two d, 3 J HF = 6.7, CF 3 CH) and -73.63 (3F, d, 3 J HF = 6.7, CF 3 CH). Found, %: Cl 15.24; S 13.41. C 6 H 8 ClF 3 O 2 S. Calculated, %: Cl 14.98; S 13.55.2-Trifluoromethyl-1,3-oxathiolan-5-one (3a). A mixture of sulfide 2a (25 g, 0.106 mol) and anhydrous zinc chloride (3 g, 22 mmol) was heated for 45 min at a temperature of 160-170°C. The reaction mixture was extracted with boiling hexane (4 × 20 ml) and the crystals that precipitated after cooling were filtered out. Compound 3a (15.6 g, 86%) was obtained; mp 61-62°C (mp 62-63°C [2]). 1 H NMR spectrum, δ, ppm (J, Hz): 3.63 (1H, dq, 2 J HH = 16.2, AB, 5 J HF = 1.2, SCH 2 ); 3.81 (1H, d, 2 J HH = 16.2, AB, SCH 2 ); 5.60 (1H, q, 3 J HF = 5.7, CF 3 CH). 19 F NMR spectrum, δ, ppm (J, Hz): -78.96 (3F, dq, 3 J HF = 5.7, 5 J HF = 1.2, CF 3 CH).4-Methyl-2-trifluoromethyl-1,3-oxathiolan-5-one (3b) was obtained as for compound 3a, as a mixture of E-and Z-stereoisomers in a 2:1 ratio. Yield 81%; bp 68-70°C (15 torr). 1 H NMR spectrum, δ, ppm (J, Hz): E-isomer: 1.69 (3H, d, 3 J HH = 7.2, CHCH 3 ); 4.05 (1H, q, 3 J HH = 7.2, CHCH 3 ); 5.59 (1H, q, 3 J HF = 5.2, CHCF 3 ); Z-isomer: 1.62 (3H, d, 3 J HH = 6.8, CHCH 3 ); 4.06 (1H, q, 3 J HH = 6.8, CHCH 3 ); 5.51 (1H, q, 3

The reaction of N-alkyltrifluoroacetimidoyl chlorides with trialkyl phosphites leads to corresponding imidoylphosphonates CF 3 C[P(O)(OAlk) 2 ]=NCH 2 R. These compounds undergo irreversible 1,3-H shift catalyzed by nitrogenous bases to give phosphorylated imines CF 3 CH[P(O)(OAlk) 2 ]N=CHR. The tendency for prototropism increases with increasing electronegativity of substituents R: CF 3 > CH 2 OMe > H > Me. N-Cyclopentyl analogs of the obtained compounds show no tendency for prototropism. Imidoylphosphonates exist mainly as Z isomers [Z/E~(6310) : 1].Imidoylphosphonates are promising synthetic precursors of biologically important derivatives of a-aminophosphonic acids. As they are the [oxidized] form of a-aminophosphonates, reduction of the C=N bond (conversion PC=N 6 PCHN) is a way of their transformation into a-aminophosphoryl derivarives.Intramolecular proton transfer that simulates biochemical transamination allows this process to be performed in the absence of a foreign reducing agent. In previous communications of this series we showed that 1,3-H transfer is characteristic of benz-[2] and some alkanimidoylphosphonates [1]. In the present ÄÄÄÄÄÄÄÄÄÄÄÄ work we synthesized (N-alkyltrifluoroacetimidoyl)-phosphonates I and considered the effect of substituents in the N-alkyl radical on the 1,3-H transfer. The electron-acceptor and simultaneously fairly chemically inert trifluoromethyl group on the sp 2 -carbon atom of compound I favors proton transfer and thus allows synthesis of phosphorus analogs of trifluoroalanine that act as enzyme inhibitors [1,3].Imidoylphosphonates I were prepared by reaction of trialkyl phosphites with imidoyl chlorides II obtained by chlorination of trifluoroacetamides III (Scheme 1). Scheme 1. ; = o ; = g O R CF 3 N R`7 76 X 2 PCl 3 ; o ; = g O R CF 3 R`7 76 I N (AlkO) 3 P ; CF 3 I g