Nitrilimines, reactions

Natural products, synthesis of 829, 835, 837, 840-842, 948, 958 Nitrile oxides, reactions of 807 Nitriles - see also y-Ketonitriles reactions of 277 synthesis of 815 Nitrilimines, reactions of 277 Nitritosulphonium intermediates 206 Nitrogen compounds, as oxidizing agents 970-972... 

The reaction is illustrated by the intramolecular cycloaddition of the nitrilimine (374) with the alkenic double bond separated from the dipole by three methylene units. The nitrilimine (374) was generated photochemically from the corresponding tetrazole (373) and the pyrrolidino[l,2-6]pyrazoline (375) was obtained in high yield 82JOC4256). Applications of a variety of these reactions will be found in Chapter 4.36. Other aspects of intramolecular 1,3-dipolar cycloadditions leading to complex, fused systems, especially when the 1,3-dipole and the dipolarophile are substituted into a benzene ring in the ortho positions, have been described (76AG(E)123). 

Reaction of 1-chloroisoquinoline with 5-phenyltetrazole gave 3-phenyl[l,2,4]triazolo[3,4-n]isoquinoline (428). It has been suggested that the initial 2-tetrazolylisoquinoline (425) underwent ring opening to (426) which readily lost N2 giving (427). This nitrilimine is a 1,5-dipole, and on cyclization the [l,2,4]triazolo[3,4-n]isoquino-line (428) is formed (70CB1918). 

Hydrazoyl halides are useful reagents for the synthesis of pyrazolines and pyrazoles (80JHC833). The elimination of HX, usually with triethylamine, is now the preferred method for the generation of the nitrilimine (621) in situ. Although in some cases it is not clear if the mechanism involves a nitrilimine (621) (as for example in the Fusco method in which sodium salts of /3-diketones are used), in other reactions it is the most reasonable possibility. For example, the synthesis of pyrazolobenzoxazine (633) from the hydrazoyl halide (631) probably occurs via the nitrilimine (632). Trifluoromethylpyrazoles (634) have been prepared by the reaction of a hydrazoyl halide and an alkynic compound in the presence of triethylamine (82H(19)179). 

Nitrilimines can be produced by treating halogenated hydrazones with a base such as triethylamine. These nitrilimines undergo 1,3 cycloaddition with enamines to form pyrazoles (181-183). This is shown by the reaction of the pyrrolidine enamine of cyclohexanone with diphenyinitrilimine to... 

The direction of addition, verified by acetylene oxidation into a known acid, proves that the nitiilimine carbon atom adds to the terminal atom of the enyne system, which is inconsistent with the assumed polarization of the unsaturated compound H2C=CH—C=C—R from the vinyl group towardR. The authors explain this by a possible transfer of the reaction center in nitrilimine as a particle with a nucleophilic center on a carbon Ph—C=N" —N —Ph Ph—C =N =N—Ph (63ZOB3558). 

The ease with which the dipolarophile interacts with vinylacetylenes depends mainly on a spatial factor. The study of the reactions of alkylthiobuten-3-ynones-l and their selenic and telluric analogs with DPNT shows that, in this case, nitrilimine also acts as a nucleophilic agent with a nucleophilic center on the carbon atom of the 1,3-dipole and always adds to the terminal carbon of the enyne system to form l,3-diphenyl-5-/ -2-pyrazolenines. The oxidation of the latter with chloranil leads to alkynylpyrazoles (65ZOR51). 

Irradiation of 3,4-diarylsydnones 329 possessing an allyl or alkenyloxy substituent provided fused dihydropyrazoles 331 presumably via decarboxylation of sydnones 329 to nitrilimine 330 and the latter s INIC reaction (Eq. 38) [94]. 

Table 20 Cycloaddition reaction of in s/ fu-generated nitrilimines with nitriles to give 1,3,5-trisubstituted 1,2,4-triazole derivatives (Equation 37)...

A 1,3-dipolar cycloaddition approach to this group of compounds involving reaction of a nitrilimine and C=N bond have already been mentioned in CHEC-II(1996) <1996CHEC-II(8)421>. Such a transformation has recently been elaborated by an English team <1994J(P1)3563> for the ring closure of the partially saturated oxazine 287 with nitrile oxide to yield the bicyclic product 288 in medium yield (42%). 

In 1981 we published the first paper [22] on the synthesis of s-triazolo[4,3-a]pyridinium salts, 4, by the anodic oxidation of hydrazones 3 in the presence of pyridine (Scheme 5). In our working mechanistic scheme we proposed nitrilimine as the possible intermediate and pointed out that this reaction opens the door to a wide range of heterocyclic systems via anodic oxidation of aldehyde hydrazones through 1,3-dipolar cycloaddition reactions of the nitrilimine involved. 

Photolysis of 3,4-diphenylsydnone gives 2,4,5-triphenyltriazole as a major product a nitrilimine is believed to be an intermediate in this reaction (Scheme 35). ... 

Dipolar additions have been extensively used for the synthesis of triazoles. The nitrilimine (166) reacts with the tetrazole (165, X = NH) to give the triazole (167). The reaction of (166) with the tetrazole (165, X = O) gives the tetrazole (168), which on treatment with base gives the tri-azolinone (169) (Scheme 31) <93JCR(S)306>. 

Most 1,3,4-oxadiazoles are thermally stable (unlike many A -l,3,4-oxadiazolines, see Section 4.06.6.2) and high temperatures are needed to induce ring cleavage. At 700°C oxadiazolinones (12) lose carbon dioxide to form a nitrilimine which undergoes further reaction, with loss of nitrogen. For example, 4-phenylbut-l-en-3-yne was formed on heating oxadiazolinone (12 R = ethynyl)... 

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