Oxathiolium salts

Reaction of 1,3-oxathiolium salts (264) with cyanamide in the presence of sodium ethoxide produces also substituted 4-aniinothiazolcs (265) (Scheme 136) (777). 

Oxathiolium salts, anhydro-5-hydroxy-thiophene synthesis from, 4, 899... 

The single report of an oxygen- and sulfur-containing five-membered ring formed from a thiourea is that of Hartmann,211 who prepared the 1,3-oxathiolium salt 91 from a-bromoacetophenone and tetramethyl-thiourea. 

Comprehensive review chapters on 1,3-oxathiolium salts <02MI35> and 1,3-oxaselenolium salts <02MI93> have appeared. Scandium triflate has been introduced as an efficient catalyst for reaction of aldehydes with mercaptoethanol to form 2-substitued 1,3-oxathiolanes <03S2503>. Protection of a-mercaptocarboxylic acids is readily achieved by... 

There have been fewer developments in the chemistry of 1,3-oxathioles and most of these have involved the saturated 1,3-oxathiolanes 7 although the synthesis of 1,3-oxathiolium salts 8 has been reviewed <2002SOS(11)35>. 

The main methods available to prepare 1,3-oxathiolium salts and their mesoionic 4- and 5-olates are of this type and were covered in CHEC-I <84CHEC-I(6)749> but two important new methods have been described. The 2-amino-1,3-oxathiolium salts (208) can be obtained by desulfurization of the phenacyldithiocarbamates (207) with a silver, mercury, or copper salt (Equation (28)) <92JAP04364178>. The l,3-dioxolium-4-olates (210) have been generated from the a-diazo anhydrides... 

There are general reviews on heterocyclic syntheses by cycloaddition reactions of isocyanates and on the use of heterocyclic cations in preparative organic chemistry. More specific topics are 5-hydroxymethylfuran-2-carb-aldehyde, isobenzofurans and related ort/io-quinonoid systems, the conversion of 2//-cyclohepta[Zj] furan-2-one (1) into derivatives of azulene, the synthesis of indoles from o-alkylphenyl isocyanides, and abnormal Fischer indolization reactions of o-methoxyphenylhydrazones. Two reviews on isoindoles have appeared and a lecture on highly conducting charge-transfer complexes that are based on heterocyclic selenium and tellurium donors has been reprinted.Recent advances in the chemistry of imidazole and in the use of nitro-imidazoles as radiosensitizers have been summarized. There have been reviews on benzimidazole A -oxides and on dihydrobenzimidazoles, benzimidazolones, benzimidazolethiones, and related compounds. Other topics are synthetic applications of 1,3-dithiolium and 1,3-oxathiolium salts and of isoxazoles, the chemistry of benzisoxazoles, 2-amino-oxazoles, 5-oxazolones (2), furoxans, benzofuroxans, and related systems, the synthesis of five-membered meso-ionic compounds, and tetrazoles. ... 

PhCOCH2SC(S)NMe2 is tranformed into the 1,3-oxathiolium salt (447) by treatment with dimethyl sulphate followed by sodium perchlorate.Monothio-benzil forms tetraphenyl-l,3-oxathiole (448) by the action of diazodiphenyl-methane.The thioamide (449) reacts with a-bromopropiophenone to yield the methyleneoxathiole (450). The action of pyridine hydrochloride on 5-(2-methoxyphenyl) AW-dimethylthiocarbamate results in the l,3-benzoxathiol-2-one (451). o-Benzoylbenzenesulphonyl chloride (452) exists as an equilibrium... 

A very promising new route to substituted thiophens has recently been developed by Hartmann. The reaction of 2-aryl-1,3-oxathiolium salts such as (33) with malononitrile in the presence of base yields 3-amino-4-cyanothiophens (34), with ethyl malonate or ethyl cyanoacetate 3-hydroxy-thiophens (34a), and finally with nitromethane 3-nitrothiophens (34b). The... 

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