Cyanogen cycloadditions

The reaction of cyanogen azide with enamines of cyclic ketones to yield a cyanoamidine with one less member in the carbocyclic ring represents a potentially valuable method of ring contraction under mild conditions (199a). The reaction probably proceeds first by 1,3 cycloaddition of the azide to the enamine followed by rearrangement and elimination of a molecule of nitrogen. 

Similarly, the regiospecific 1,3-dipolar cycloaddition reaction of 1-methyl-1,2-dihydropyridines 41 with cyanogen azide (50a) and selected organic azides 50c and 50g afforded 2-methyl-2,7-diazabicyclo[4.1.0]hept-4-enes 57, which can be elaborated to 1-methyl-l,2,5,6-tetrahydropyridylidene-2-cyanamide (58) and 1-methyl-2-piperidylidenes 59a-d (85CJC2362). 

Cycloadditions to a cyano group are comparatively rare. The high-temperature reactions of 1,3-dienes, e.g. butadiene, isoprene and 2-chloro-l,3-butadiene, with dicyanogen, propionitrile or benzonitrile result in formation of pyridines (equation 80)70. Sulfonyl cyanides 147, obtained by the action of cyanogen chloride on sodium salts of sulfinic acids, add to dienes to give dihydropyridines 148, which are transformed into pyridines 149 by oxidation (equation 81)71. 

D-Triazoles have been isolated from the reaction of several activated nitriles, such as cyanogen, cyanogen halides, methyl cyanoformate, and cyanic acid esters, with diazoalkanes. The reaction can formally be regarded as a 1,3-dipolar cycloaddition. The v-triazoles may be... 

Nonactivated nitriles undergo cycloaddition with especially reactive nitrile oxides (e.g., trifluoro-acetonitrile oxide <84JOC919> or bromocyanogen oxide <89JHC23>, acylcyanide oxides <87JHC697>, or cyanogen monooxide (Equation (31)) <91IZV1916>. 

Irradiation of 2,3-diphenyl-2//-azitine in the presence of Cgo fullerene leads to the formation of mono- and ohgo adducts (98,99). A monoadduct, l,9-(3,4-dihydro-2,5-diphenyl-2//-pytTolo)fullerene-60 was isolated and characterized. Mechanistic studies showed that under conditions of direct irradiation it was formed by a classic nitrile yhde cycloaddition but in the presence of 1,4-napthalenedicarbonitrile (DCA) it resulted from reaction of the radical cation intermediate 108. Cycloaddition reactions have also been carried out with diaza-phospholes and diazaarsoles (100) to give adducts of the type 189 (A=As,P) and with cyanogen to give 190 and with atyldiazocyanides where addition to both the azo moiety and the cyano group were observed (101). 

The formal criss-cross cycloaddition product of cyanogen with sulfur trioxide (molar ratio 1 2) has been shown to be l,2,3-oxathiazolo[5,4-d][l,2,3]oxathiazole 2,2,5,5-tetroxide (5). The S—O bond in the ring is extremely long at 1.71 A, while the exocyclic S=0 bonds are shortened to 1.39 A, suggesting a description of the molecule in terms of bond-nonbond resonance, the resonance formulae (5a) and (5b) also providing some rationalization for the short C—O bond (1.29 A) (79AG(E)223). 

Chlorosulfonyl isocyanate6 (CSI) (57) is a very reactive compound which was first prepared from cyanogen chloride (56) and sulfur trioxide (Graf, 1956) (Scheme 31). CSI (57) undergoes [2+2] cycloaddition reactions with various alkenes initial adducts like (58) and (59) may be hydrolysed to the b-lactams (60) and (61). The cycloaddition reaction also occurs with enamines (62) to give products like (63) and (64) (Scheme 32). 

Cycloaddition Cyanogen azide. Ethyl azidoformate. Tetracyanoethylene (cyclobutane formation). Trimethylsilyl azide. 

Kinetic data on addition reactions, and their implications as to the reaction mechanism, have been reviewed in the recent past this is particularly true for the Diels-Alder reaction - - and its reverse reaction , and for 1,3-cyclo-additions . As well, kinetics and mechanism have been reviewed for particular cases, like Diels-Alder reactions of cyanogen and nitroso derivatives as dienophiles, and of cyclopentadienones as dienes. Other discussions of mechanism, of the Diels-Alder reaction and of 1,2-cycloadditions - , are also worth noting. Another particular case is that of 1,3-cycloadditions of nitrile oxides ", ... 

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