1.2.4- Thiadiazolidines 2.4- dialkyl

The IR spectrum of 1,2,4-thiadiazolidine-3,5-dione indicates that the dithione structure (13) predominates. However, the dithione can be readily dialkylated on sulfur and treatment with 1-chloro-4-nitrobenzene in aqueous sodium hydroxide yields (150) (Scheme 33) <89EUP330020>. 

Thioxo-1,2,4-dithiazolidines can be obtained from thioxo-l,2,4-thiadiazolidines by Dimroth rearrangement (Scheme 47) or reversibly by addition and elimination of acetone (Scheme 22). 1,2,4-Dithiazole type products are also obtained from thiocarbonyl isothiocyanates (154) by reaction with CI2 <84CHEC-I(6)897>, PhMgBr, Sj, or CS2. Other routes include reactions of carbonyl isothiocyanates and thiocarbonyl isocyanates with P4S10 or Sg <84Chec-I(6)897> and sulfonyl isocyanates with dialkyl thioketenes. Phenylisothiocyanate heated with N,C-disubstituted oxaziridines affords 3,5-diimino-l,2,4-dithiazolidines (226, 227). Other miscellaneous syntheses of 1,2,4-dithiazoline derivatives include cyclization of A7-thioacyl hexafluoroacetonimine to 5,5-bis(trifluoromethyl)-... 

R = Et) yields, by the familiar Hugershoff cyclization,114 the substituted benzthiazole 128 and not the thiadiazolidine 129. In 1,5-dialkyl-aryl group suitable for benzthiazole formation, oxidation by iodine or bromine causes mainly S-dealkylation and subsequent formation of cyclic disulfides (126)137 in two cases, however, the formation of thiadiazolines (129 R = PhCH2, R = Me, R" = Me or Et and R = CH2=CHCH2, R=p-C6H4Me, R" = Me)137-138 as additional products in undisclosed yields, has been observed. 

The IR spectrum in Nujol of l,2,4-thiadiazolidine-3,5-dithione indicates that the dithione structure (18a) predominates. However, the dithione can be readily dialkylated on sulfur. Thus, treatment with 2,3-dichloropropene in aqueous sodium hydroxide forms (208 Scheme 73) (65AHC(5)119). The disulfenamide (209) condenses with aldehydes and ketones to give the corresponding imines (210) and (211 Scheme 74) (74ZOB2553). 5-Mercapto-3-methyl-thio-l,2,4-thiadiazole (212) reacts with di- -butyltin chloride in THF to give di-n-butyltin derivative (213 Scheme 75) (72USP3634442). 

The chemical shifts for a large number of 2,5-dialkyl-l,3,4-thiadiazoles are known (73ACS391) and selected compounds are shown in Table 1 (for the proton NMR spectra of thiadiazolidines see (80JCS(P1)574)). 

Table 8 1H NMR Chemical Shifts for 5,5-Dialkyl-l,3,4-thiadiazolidine-5-thiones and Their Precursor (70ACSI79) ...

Ruhlmann prepared 2,5-dialkyl-l,3,4-thiadiazoles (6) in high yields via 1,3,4-thiadiazolidines (8). These were obtained from hydrazine, hydrogen sulfide, and aliphatic aldehydes, and they were oxidized to 6 by sulfur in boiling piperidine. 

Tributylphosphine. The adduct between BU3P and CS2 is readily formed in CH2CI2, and reacts with dialkyl azodicarboxy-lates and aldehydes to give l,3,4-thiadiazolidine-2-thiones (24) in 36-86% yields (eq 17). ... 

The A -1,3,4-thiadiazolidines (148) undergo cycloaddition with diethyl azodicarboxylate stereospecifically, forming 2,5-dialkyl-3,4-diethoxy-carbonyl-1,3,4-thiadiazolidines (154) with complete retention of configuration. The comparable stereospecific cycloaddition involving dimethyl acetylenedicarboxylate, (152) (153), yields the corresponding 2,5-dihy drothiophens. ... 

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