Isothiocyanates nitrile oxides

In a manner analogous to classic nitrile iinines, the additions of trifluoro-methylacetonitrile phenylimine occur regiospecifically with activated terminal alkenes but less selectively with alkynes [39], The nitnle imine reacts with both dimethyl fumarate and dimethyl maleate m moderate yields to give exclusively the trans product, presumably via epimenzation of the labile H at position 4 [40] (equation 42) The nitrile imine exhibits exo selectivities in its reactions with norbornene and norbornadiene, which are similar to those seen for the nitrile oxide [37], and even greater reactivity with enolates than that of the nitnle oxide [38, 41], Reactions of trifluoroacetomtrile phenyl imine with isocyanates, isothiocyanates, and carbodiimides are also reported [42]... 

Cycloaddition of 2-nitrosopyridine 48 with nitrile oxides can give either di-A -oxides such as 49 or 3-mono-A -oxides such as 50 (93JHC287). In general, greater electron withdrawing character in the aromatic substituent appears to favor formation of the di-A -oxides. Sulfur ylides such as compound 51 are obtained from aryl isothiocyanates and l-amino-2-methylthiopyridinium iodides (84JCS(P1)1891) nitrogen ylides can be obtained from a similar reaction (86H(24)3363). 

A cycloreversion mechanism is suggested for the transformation of the nonisolable cycloadduct 90 to the aldehyde 91 and isothiocyanate 92 <1996BCJ719> and for the spiro-1,4,2-oxathiazole intermediates 94 to the dioxothiazoline 95 and the aryl isothiocyanate 92 <2001MOL510>. Both cycloadducts are obtained by cycloaddition reactions of nitrile oxides 88 to thiocarbonyl compounds (Scheme 12). 

In recent years remarkable progress has been made in the chemistry of organosilicon compounds containing a double bond to group 14 and group 15 elements. The reaction of a silylene-isocyanide complex with nitrile oxide generated the intermediate silanone, which with phenyl isothiocyanate afforded 1,3,2-oxathiasiletane 63, which is sensitive to hydrolysis (Equation 10) <2000CL244>. 

Isothiocyanates. Both a-chloro aldoximes and nitroalkanes give isothiocyanates on reaction with thiourea. The former needs a base (e.g., E N) to generate nitrile oxides in situ, and the latter requires both a base and a dehydrating agent, such as 4-chlorophenyl isocyanate. 

TABLE 8. Complex of nitrile oxides, organic thiocyanates, isocyanates and isothiocyanates with transition metals... 

Far more interesting are the elimination sequences which lead to the generation of reactive heterocumulenes (ketenimines, carbodiimides, isocyanates, isothiocyanates) or 1,3-dipoles (nitrile oxides, nitrile imides, nitrile... 

Reviews of the Cope reaction, electronic quantum fluxes during the rearrangement of semibullvalene," the chemistry of hetero-substituted isocyanates and isothiocyanates RX-NCY (X = R2N, RO, RS Y = 0, S) and the isomeric cyanates RX-OCN, thiocyanates RX-SCN, nitrile oxides RX-CNO, and nitrile sulfides RX-CNS have appeared. ... 

Nitrile oxides react with carbon disulfide to give the [3+2] cycloadduct 62 which reacts with a second equivalent of the nitrile oxide and, with elimination of isothiocyanates gives the carbonyl sulfide cycloadduct 63 ". ... 

The oxidation of thioamides 63 with a wide variety of oxidizing agents is a well-employed method for the synthesis of 3,5-disubstituted-l,2,4-thiadiazoles 64 <1982AHC285>. However, this method is limited mainly to arylthioamides. The most common oxidizing agents tend to be halogens, hydrogen peroxide, dimethyl sulfoxide (DMSO), and nitrous acid. Yields from these reactions are variable and depend on the thioamide, oxidant, and conditions used (Equation 19). By-products such as nitriles and isothiocyanates are usually formed. 

The UV spectrum of the 3-oxide in ethanol exhibits maxima at 254 nm (e = 19300) and 320 nm (e = 3000), the latter appearing as a shoulder. On irradiation (A = 250 nm, in methylene chloride), benzo-nitrile and phenyl isothiocyanate are formed in 65% and 3% yields, respectively. A similar result is obtained on photolysis of 5-phenylthiatri-azole (Section III, C). The major part of the products was shown to be formed from the singlet excited state.23... 

Functional group transformations. Dimethyldioxirane effects conversion of isothiocyanates to isocyanates," TV, Al-dimethylhydrazones of aldehydes to nitriles, and the oxidative cleavage of nitronate ions (Nef reaction) with relative ease. Regioselective oxidation of diols and triols is also achieved. " ... 

Simple addition, in which both fragments of the NH molecule enter the new compound as in the preparation of alkanolamines from alkylene oxides, aminonitriles from unsaturated nitriles, and ureas and thioureas from isocyanates and isothiocyanates. 

The 1,3-dipolar character of triazaallenium salts, from now on referred to as l,3-diaza-2-azoniaallene salts, is evidenced by the many [3+2] cycloaddition reactions these types of compounds can participate in. The l,3-diaza-2-azoniaallene salts are generated in situ and trapped with suitable dipolarophiles. For example, l,3-diaza-2-azoniaallene salts undergo stereospecific [3+2] cycloaddition reactions with alkynes and olefins. However, they fail to react with isocyanates, isothiocyanates and azo compounds. Also, [3+2] cycloadditions to carbodiimides and cyanamides are observed. In contrast, nitriles fail to react. 1,3-Diaza-2-azoniaallene salts are obtained in the oxidation of 1,3-disubstituted triazenes with t-butyl hypochlorite. The resultant Al-chlorotriazenes react with antimony pentachloride to form the salts as reactive intermediates. Above —25°C, l,3-diaza-2-azoniaaUene salts disproportionate into diazonium salts and azo compounds. 

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