Nitriles, Isocyanates, Isothiocyanates, and Imines

Nitriles, isocyanates, and isothiocyanates all have y p-hydridized carbon atoms similar to the C C bond. They absorb in the region 2100-2270 cm . The C=N bond of an imine has an sp carbon atom, however. Imines and similar compounds absorb near where double bonds appear, 1690-1640 cm .  

FIGURE 2.62 The infrared spectrum of butyronitrile (neat liquid, KBr plates). 

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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]... 

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). 

Cycloaddition of 1,2,4,5-tetrazines with C-N double or triple bonds yields dihydro-1,2,4-tri-azines 13 or 1,2,4-triazines 14 (see Section B.2.2.1.3.). Various systems with C—N double bonds have been used imines, including dihydropyrroles and dihydroisoquinolines 341 344 hydra-zones, including dihydropyrazoles,343 348 oxime ethers,343 imidates, including dihydrooxa-zoles 345 357 thioiniidates, including dihydrothiazoles 345,349,350 357 358 amidrazones 357,358 amidines 359 and isocyanates or isothiocyanates.351 Nitriles are the examples of systems with a C-N triple bond.352 -356... 

The methods for generating acyl ketenes (Scheme 7-V) and their subsequent in situ participation in [4 + 2] cycloadditions with a wide range of hetero- or olefinic and acetylenic dienophiles (Scheme 7-VI), including acyl ketenes,185 186,197 carbonyl compounds, 86-188 nitriles,1874,189,191 isocyanates and isothiocyanates,1864,190,191 ketenes,191 imines,1864,1874,191,192 carbo-diimides,l87c 190,191,193 ynamines,194 ketene acetals,1864,195 enol ethers,1864,191,196 and V-sulfinylamines197 have been extensively reviewed.5,9,12 Two reports have detailed the 4-n- participation of allenic ketones in [4 + 2] cycloaddition reactions [Eq. (51)].198,199... 

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