Heterocumulenes isothiocyanates

Corriu et al. also described an alternative synthetic method for internally coordinated silanethiones starting from the pentacoordinated diaminosilanes.28 As shown in Scheme 9, the pentacoordinated diaminosilanes 32 are allowed to react with sulfur-containing heterocumulenes such as carbon disulfide or phenyl isothiocyanate to give the corresponding insertion products 33, which undergo thermal decomposition to produce the corresponding silanethiones 31, 34, and 35.28... 

The synthetic route to 1,3,4-oxadiazines and 1,3,4-thiadiazines (Scheme 105) begins with the iminophosphorane of imidazolone 294, which is converted with isocyanate or isothiocyanate to carbodiimide 295. A second addition of the heterocumulenes occurs to the CH acid at the 5-position,... 

Numerous further synthetic applications can be envisaged. Amines add to heterocumulenes. For example, the isothiocyanates 161 give a great number of thioureas in quantitative yield with gaseous or solid primary and secondary amines that are listed in Table 4 [12]. All thioureas are obtained with 100% yield directly in pure form (Scheme 19). 

In contrast to 4-alkyl-5-sulfonylimino-A -l,2,3,4-thiatriazolines (58) (Section 4.19.5.1.2), 4-alkyl-5-alkylimino-A -l,2,3,4-thiatriazolines (50) react with immediate nitrogen evolution when added to electron-rich alkenes or to heterocumulenes such as enamines, carbodiimides, isocyanates, isothiocyanates, or styrene. Reaction kinetics for certain of this type of system show that they undergo bimolecular processes as described below. 

Diazo(trimethylsilyl)methyl lithium (3) was found to be the reagent of choice for the synthesis of azoles from heterocumulenes (Scheme 8.43). The reaction is typically carried out in ether at 0-20 °C. Thus, alkyl- (or aryl-)substituted keteni-mines are transformed into 1,2,3-triazoles 188 (246), while C-acceptor-substituted ketenimines yield either 4-aminopyrazoles 189 or 1,2,3-triazoles, depending on the substituents (247). Isocyanates are converted into 5-hydroxy-1,2,3-triazoles 190 (248). Reaction of 3 with isothiocyanates are strongly solvent dependent. 

Iminophosphoranes have also proved to be key intermediates because they react with carbonyl compounds, isocyanates, isothiocyanates, acid chlorides, carbon dioxide, and carbon disulfide to give a wide range of imines and heterocumulenes, which are intermediates to pteridines. The preparation of iminophosphoranes has been investigated... 

N-Vinyl heterocumulenes represent a new, highly reactive 2-azadiene species, which react, in general, with electron-rich alkenes and alkynes. Accordingly, we think it is of interest to complement the utility of electron-poor 2-azadienes in [4 + 2] cycloadditions by showing some examples involving A-vinyl isocyanates, -isothiocyanates, -carbodiimides, and -ketenimines. 

Isocyanates and isothiocyanates are highly reactive heterocumulenes, and are usually only prepared on solid phase as intermediates for the synthesis of ureas, carbamates, thioureas, etc., using methods similar to those used in solution (Table 14.2). 

Isocyanate and isothiocyanate carbon nuclei resonate between 120 and 130 ppm [77a]. Isothiocyanate carbons are slightly deshielded relative to comparable isocyanates. Typical nitrile shift values (110-115 ppm) are characteristic of thiocyanates (rhodanides), while the carbon nuclei of rhodanide and cyanate anions shift to lower field due to significant contributions of heterocumulene-type resonance formulae. 

The method based on the reaction of 3-bromo-2-cyanomethylpyridine (175, X = CN) or ester 175 (X = COOEt) with heterocumulenes, such as phenyl isothiocyanate or CS2 (1992S528, 1997S949, 1998S1095) is of interest. The reaction... 

This approach to 1,2,4-dithiazolidine derivatives 124 was investigated in detail by L abbe and co-workers on the example of a reaction of 4-alkyl-5-arylimino-l,2,3,4-thiotriazolines 123 and related compounds with isothiocyanates and other heterocumulenes. In these reactions, in addition to compounds 124, l,2,4-thiadiazolidine-3-thiones 125 are formed (Equation 17) <1996CHEC-II(4)453>. 

Fig. 8.11. Tandem reaction consisting of three single reactions mutually transforming heterocumulenes and heteroatom nucleophiles in a one-pot synthesis of an isothiocyanate (1) uncatalyzed addition reaction of heteroatom nucleophile (aniline) + heterocumulene (carbon disulfide) —> carbonic acid derivative (A) (2) heterolysis-initiated /3-elimination of the carbonic acid derivative (D) -> heterocumulene (F = phenylisothiocyanate) + heteroatom nucleophile (thiocar-bonic acid O-ethylester) (3) decomposition of a carbonic acid derivative (D) to a heterocumulene (carbon oxysulfide) and a heteroatom nucleophile (ethanol) via the zwitterion H.

The ruthenium complex Cp RuCl(COD) catalyzed the [2+2+2] cycloaddition of 1,6-diynes with heterocumulenes such as isocyanates, isothiocyanates, or carbon disulfide [99,100]. Bicyclic pyridones [99] and bicyclic thiopyrans [100] were thus obtained (Eq. 76). 

In the absence of dipolarophiles the intermediate loses sulfur to give the carbodiimide however, the intermediate may be trapped with a number of alkenes, heterocumulenes and other reagents such as ynamines, ketenes, isocyanates, isothiocyanates, carbodiimides, ketenimines, sulfonylimines, imines, nitriles, thiocarbonyl compounds, Wittig reagents and the already mentioned enamines (80AG277). Contemporary knowledge of the chemistry of these sulfonyliminothiatriazolines is mainly due to the meticulous work of L abbe and his coworkers (80AG277). 

The palladium-catalyzed [3 + 2] cycloaddition of vinylic oxirane 20a [42] and aziridine 20b [39] with the activated olefin 4a for the formation of five membered cyclic ether 21a and pyrrolidine derivative 21b has also been reported in our laboratories. The mechanistic issue is very much similar to that discussed in Scheme 9. Pd(0) catalyst added oxidatively to 20 to produce the 7r-allylpalladium complex 22. The Michael addition of a hetero nucleophile in 22 to the activated olefin 4a gives 23 which undergoes intramolecular nucleophilic attack on the inner 7r-allylic carbon atom to give the cy-clized products 21 and Pd(0) species is generated (Scheme 10). Similarly, the palladium-catalyzed [3 + 2] cycloaddition of vinylic oxirane 20a with the N-losylimincs 24 is also known (Scheme 11) [43]. Intermolecular cycloaddition of vinyl epoxides and aziridines with the heterocumulenes such as isocyanates, carbodiimides and isothiocyanates is also known [44,45]. Alper et al. reported the regio- and enatioselective formation of the thiaolidine, oxathiolane, and dithiolane derivatives by the palladium-catalyzed cyclization reaction of 2-vinylthiirane with heterocumulenes [46]. 

By Aza-Wittig Reaction. In the reaction of heterocumulenes with iminophos-phoranes, carbodiimides with different substituents on nitrogen are obtained. The reaction of iminophosphoranes 61 with isocyanates (X=0) or isothiocyanates (X=S) to give carbodiimides with two different substituents 62 was discovered by Staudinger and Hauser in 1921.102... 

Symmetrically substituted carbodiimides are also obtained from iminophosphoranes and carbon dioxide or carbon disulfide, involving isocyanates or isothiocyanates as intermediates. Instead of the heterocumulenes di-t-butylcarbonate is also used in the reaction with iminophosphoranes. For example, bis(l-naphthyl)carbodiimide is obtained in 64 % yield using this procedure. 

The insertion reaction of heterocumulenes can be used to syuthesize carbodiimides having two different substituents. For example, the carbamate 157 derived from an isocyanate and bis(tributyltin)oxide can be reacted with an isothiocyanate to give a carbodiimide 158 with substituents derived from the isocyanate and the isothiocyanate. ... 

Heterocumulenes undergo insertion reactions with numerous substrates. In general, carbodiimides react faster than isocyanates and isothiocyanates, in that order. Insertions of carbodiimides into metal-hydrogen, metal-halogen, metal-mitrogen, metal-oxygen and metal-sulfur bonds are reported. Also insertions of carbodiimides into carbon-hydrogen bonds are known. 

Carbodiimides also play a role as building blocks of numerous N-heterocycles. Examples are the cycloaddition reactions of carbodiimides. In the formation of [2-1-2] cycloadducts N-methyl-N -t-butylcarbodiimide is used as a marker to determine the mode of addition of isocyanates or isothiocyanates to carbodiimides. In these reactions addition across the C=N or the C=0 bond of the isocyanate or across the C=N or the C==S bond of the isothiocyanate can occur. Addition to the N-methyl-N -t-butylcarbodiimide always proceeds across the N-methyl double bond. Also, theretroreaction of the [2-1-2] cycloaddition reaction of carbodiimides can afford a different set of heterocumulenes. ... 

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