1.2.5- Thiadiazolidine 1-oxide

PhNHC(=NPh)C(=NPh)Ph SOC12 2,5-Diphenyl-3,4-diphenylimino-1,2,5-thiadiazolidine 1-oxide 80JPR273... 

The problem of the synthesis of highly substituted olefins from ketones according to this principle was solved by D.H.R. Barton. The ketones are first connected to azines by hydrazine and secondly treated with hydrogen sulfide to yield 1,3,4-thiadiazolidines. In this heterocycle the substituents of the prospective olefin are too far from each other to produce problems. Mild oxidation of the hydrazine nitrogens produces d -l,3,4-thiadiazolines. The decisive step of carbon-carbon bond formation is achieved in a thermal reaction a nitrogen molecule is cleaved off and the biradical formed recombines immediately since its two reactive centers are hold together by the sulfur atom. The thiirane (episulfide) can be finally desulfurized by phosphines or phosphites, and the desired olefin is formed. With very large substituents the 1,3,4-thiadiazolidines do not form with hydrazine. In such cases, however, direct thiadiazoline formation from thiones and diazo compounds is often possible, or a thermal reaction between alkylideneazinophosphoranes and thiones may be successful (D.H.R. Barton, 1972, 1974, 1975). 

An approach to 2,3,5-triaryl-4-imino substituted 1,2,5-thiadiazolidin 5-oxides 242 is the cycloaddition reaction between A -(a-cyano-a-aryl)-methylanilines 240 and sulphinylanilines 241 (99SC(29)911). In this way a number of thiazoli-dine S-oxides 242 could be obtained in satisfactory yield (54-70%). 

The number of X-ray structures published since the publication of CHEC-II(1996) has increased, underlining the importance of this technique in structure elucidation. The structure of a number of 1,2,4-thiadiazoles and 1,2,4-thiadiazolidines has been determined by X-ray techniques and they are listed in Table 1. The first preparation of an A7-oxide derivative of a 1,2,4-thiadiazole 2 has been reported. The X-ray structure of compound 2 shows that it has a nearly planar ring this conformation is stabilized by hydrogen bonding with the carboxamide group <1999J(P1)2243>. 

Treatment of enantiomerically pure (R,R)- and (A,A)-l,2-bis(pentafluorophenyl)ethane-l,2-diamines with thionyl chloride gave the corresponding thiadiazolidine 1-oxides in high yield <2004BCJ1001>. A series of Aralkyl-substituted thiadiazolidine 1,1-dioxides 171 were also prepared from the starting 1,2-diamine 170 by treatment with sulfamide followed by a regioselective monoalkylation (Scheme 26) <2005BML4212>. 

The anodic oxidation of substituted allenes [76-79] and hetero-allenes [80-85] has been extensively studied by Becker and coworkers. Oxidation of secondary and tertiary alkyl isothiocyanates resulted in an ot-cleavage processes [77]. Primary alkyl isocyanates yielded amides and carbonyl compounds due to the nucleophilic involvement of either acetonitrile or water [80]. Primary alkyl isothiocyanates 48 afforded five-membered thiadiazolidine 49 and 50 and... 

A similar transformation occurs when 5-imino-3-oxo-l,2,4-dithiazolidine (300) is treated with neat benzylamine to give 2-benzyl-3-oxo-5-imino-l,2,4-thiadiazolidine (301). When the reaction is carried out in ethanolic solution the thiobiuret (302) is formed which can then be oxidized to (301) (Scheme 68) <82JIC71>. 

Bu NHCOCHjNHPh SOCI2 2-r-Butyl-5-phenyl-1,2,5-thiadiazolidin-3-one 1-oxide 77JOC1015... 

Peroxide oxidation of 2-imino-l,3-thiazetidine does not lead to simple sulfur oxidation. Oxidative cleavage and ring closure result in 3-oxo-l,2,4-thiadiazolidine 1-oxide formation (Scheme 27) (76AG(E)103). 

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. 

Compounds of molecular formulae (RNCS)20 and (RNCS)2S, for which 1,2,4-thiadiazolidine structures have been considered, are obtainable from isothiocyanate esters on oxidation the latter series is also accessible from dithiocarbamates. 

The experimental evidence as a whole suggests that both isothiocyanate oxides and sulfides, in the form of their salts, possess the dithiazolidine structures 153 and 155, respectively the lower alkyl isothiocyanate oxides when liberated rearrange to the 1,2,4-thiadiazolidines (152), but the higher homologs do not. In the isothiocyanate sulfides,... 

Isomerization of this cyclic disulfide (see above) affords the 1,2,4-thiadiazolidine (159), also obtainable directly from sodium methyl dithiocarbamate by conveying the wet, finely powdered salt under oxidative conditions through a pneumatic dryer.166 The production of alkyl (and phenyl) homologs by this procedure is claimed in the patent literature,166 but no physical constants are given. It is recalled that the isomerization 158->159 had previously been thought to be confined to the methyl homologs.160,164... 

The oxidation of dithiobiuret and its homologs yields the so-called thiurets (for asummary, see ref. 134), for which a 1,2,4-dithiazolidine structure (319 and 320) is generally accepted. Their formulation as 3-thiono-l,2,4-thiadiazolidines (317 and 318) has been discussed,1 but the weight of the available evidence supports the cyclic disulfide structure (319 and 320)184 originally proposed.188... 

The preparations of 1,2,4-thiadiazoles and 1,2,4-thiadiazolidines from thioureas are well known and have been summarized in three reviews those of Bambas,188 Sherman,189 and Kurzer.170 Contained in these reviews are discussions of the controversies that surrounded some of the products, notably Hector s bases, which resulted from oxidation of substituted thioureas.171,172 Subjects covered in the above reviews, but too extensive to outline in detail here, are the oxidation of amidinothioureas to 3,5-diamino-1,2,4-thiadiazoles (71),173,174 the oxidation of phenylthiourea175 and of substituted amidinothioureas176 to 3,5-diimino-l,2,4-thiadiazolidines (72, Hector s bases), the reaction of thiopseudoureas with trichloromethanesulfenyl chloride to form 3-alkylthio-5-chloro-l,2,4-thiadiazoles (73),177 the reaction of thiopseudoureas with sodium thiocyanate and bromine178 and the oxidation... 

Tetrahydrothiopyran-4-one undergoes a Barton-Kellogg reaction with hydrazine hydrate to give the azine 370. Sequential thiadiazolidine formation, oxidation to the thiadiazoline and extrusion of N2 produces the 4,4 -bis(tetra-hydro-4/7-thiopyranylidene) (Scheme 91) <2000JOC4584>. 

The X-ray crystal structures for [l,2,5]thiadiazolo[3,4-g]benzofurazan 1-oxide (77AX(B)3685), 2,5-diphenyl-(l-phenylimino)-l,2,5-thiadiazolidine-3,4-dione (77CB3149), 7-amino-[l,2,5]thiadiazolo[3,4-d]pyrimidine <71JA728l), 2,3,3,5-tetraphenyl-l,2,5-... 

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