Isothiocyanates reaction with carbenes

In Section 1.2, we indicated that the nucleophilic properties of dimethoxy-carbene could be put to synthetic use for example in the synthesis of heterocyclic compounds by reactions with isocyanates and isothiocyanates. [23,24] It is worth noting that analogous chemistry is being elaborated by Rigby s group forthebis(alkylthio)carbenes e.g., ( -PrS)2C. [109] Obviously, the nucleophilic properties of (RS)2C parallel those of (MeO)2C. Moreover, further manipulation of the alkythio groups in the products of (RS)2C reactions opens substantial synthetic opportunities. [109]... 

Encouraged by our results on stoichiometric and catalytic metathesis reactions of carbodiimides and imines with Fischer type carbene tungsten(O) complexes (9) we started 1984 with metathesis like reactions of the Schrock type carbyne tungsten (VI) complex Cl3(dme)WCtBu with heteroallenes (isocyanates, carbodiimides, isothiocyanates) and with heteroalkenes (imines and nitroso compounds). 

Carbenes can also participate in [1+2+2] cycloaddition reactions, in these reaction, ionic intermediates are formed, which can be intercepted by a second molecule of the isothiocyanate. For example, dimethoxycarbene, formed in the thermolysis of 1,2,3,4-tetrachloro-7,7-dimethoxy-5-phenylbicyclo[2.2.1]hepta-2,5-diene 11, reacts with excess aryl isothiocyanate to give the [1+2+2] cycloadducts 12. The initial reaction of dimethoxycarbene with the aryl isothiocyanate generates a 1,3-dipole, which undergoes a [3+2] cycloaddition reaction with the second equivalent of the aryl isothiocyanate... 

The ambident 1,3-dipolar 2-arylthiocarbamoyl imidazolium salts 859 are readily prepared from the corresponding carbenes and phenyl isothiocyanate as crystalline solids. Reaction of 859 with DMAD leads to the formation of spiro[imidazoline-2,3 -dihydrothiophenes] 860, indicating that 859 acts as a C-C-S dipole. In contrast, the reaction of 859 with ethyl propiolate proceeds slowly to form spiro [imidazoline-2,3 -dihydropyrroles] 861, indicating a C-C-N dipolar reaction being thermodynamically driven (Scheme 211) <2006CC1215>. 

Related reactions of thiolate anions with ort/zo-chloromethyl-phenyl(diphenyl)phosphine have provided a range of ort/ o-alkyl and aryl-thiomethylphenyl(diphenyl)phosphines. " The reactions of 2-amino-alkylphosphines with isocyanates and isothiocyanates have provided routes to new chiral phosphinoalkyl-urea and -thiourea ligands. Similarly, treatment of hydroxy- or amino-functional arylphosphines with isocyanides in the presence of a cyclooctadienepalladium(II) complex results in the formation of bidentate arylphosphino-carbene palladium complexes. New chiral phosphinoarylphosphoramidite ligands, e.g.,... 

The enantioselective A-heterocyclic carbene-catalysed formal 2 + 2- and 2 + 2 + 2-cycloadditions of ketenes with isothiocyanates have been investigated. At room temperature, the reaction of A-arylthiocyanates favours the 2 + 2-cycloaddition. However, at -40 °C, A -benzoyiisothiocyanates undergo the 2 + 2 + 2-cycloaddition. ... 

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