Isothioureas, cyclic

Cyclic isothioureas 168 were prepared simply by reaction of 1,3 diamines 167 and CS2 in EtOH under microwave irradiation at 140 °C with elimination of one molecule of H2S (Scheme 60). 

The aza-Diels-Alder reaction of a variety of amino-aza-heterocycles to yield cyclic amidines and isothioureas has been reported <1996TL2619>. 

Conversion of the diamine of 52 to a guanidine proved very challenging. Reaction of 52 with thiophosgene26 afforded cyclic thiourea 53 in only 40% yield and initial attempts to convert 53 to the guanidine were unsuccessful. Reaction with methyl iodide in MeOH at reflux afforded isothiourea 54, which did not form the desired guanidine on treatment with ammonia in MeOH. 

Aminobenzothiazoles undergo reaction with formaldehyde and electron-rich alkenes such as cyclopentadiene (Scheme 8) to give a cyclic isothiourea 61 with regio- and stereoconttol <1996TL2619>. 

In addition to cyclization of 2-mercaptoadenines with dibromoethane to a mixture of [2,3-Z>] and [3,2-a] isomers (86, 85) shown in Scheme 23, the method starting from 2-aminothiazole also produced this heterocycle. This compound—a cyclic isothiourea—was condensed with ethyl nitrosocyanoacetate to 5-amino-6-nitroso-thia/o 1 o[3,2-nitroso group with sodium dithionite to 6-amino derivative 91 followed by acylation with acyl chloride yielded 5-amino-6-acylaminothiazolo[3,2-u]pyrimidin-7-one (92). Heating 92 with polypho-sphoric acid produced 2-aryl- or 2-heteroaryl-thiazolo[2,3-/)]purin-4(3//)-ones 93. 

Isothioureas (179) heated with lA in aqueous media give quinazoline-diones (180). Heating in dry solvents (e.g. DMF) leads to quinazolinones 181 212,218-222 jg2 211,223 pj. 1 3211.212.220 (Scheme 30). Cyclic isothioureas... 

Abstract The high synthetic versatiUty exhibited by the isothiocyanato motif has allowed its use as a building block in the preparation of a plethora of derivatives. When present in carbohydrates, the strong electrophilicity shown by isothiocyanates, together with the possibility of undergoing cycloaddition reactions has made it possible to access a broad spectrum of heterocyclic compounds, of either synthetic or pharmaceutical interest. Among them, noteworthy are 1,3-oxazolidine- and l,3-oxazinane-2-thiones (cyclic thiocarbamates), 2-amino-2-oxazolines (cyclic isoureas), 2-amino-2-thiazolines (cyclic isothioureas), nucleosides, and spironucleosides. 

The bicyclic compound (121) may be regarded as a more rigid derivative of type (95) and may also be looked upon as a cyclic isothiourea derivative. Like (95), compound (121) antagonized also reserpine and potentiated DOPA (mice) [257]. Related to (121) is a series of acetic acids and esters represented by (122),... 

Mercuric acetate sulfuric acid N-Condensed cyclic isothioureas from 2-acetylenethioethers... 

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