Nitrone cyanation

Finally, nitrone cyanation were performed with non-chiral urea and thiourea derivatives, the latter being more efficient for this process. No chiral compound has been described yet (Scheme 41) [ 159]. 

Addition of Ketene Acetals and Enoles In recent years, much attention has been given to the synthesis of optically active nitrogen-containing compounds, with the key step being the highly stereoselective nucleophilic addition of ketene silyl acetals to nitrones (Scheme 2.174). Similar to nitrone cyanations, in ketene silyl acetal reactions one observes an accelerating effect with thiourea derivatives (633). 

QUINOXALINE CYANATES, ISOCYANATES, THIOCYANATES, ISOTHIOCYANATES, AND NITRONES... 

There is virtually no recent literature on quinoxaline cyanates or isocyanates, and most of what little there is on quinoxaline thiocyanates, isothiocyanates, or nitrones has been covered already the preparation of thiocyanatoquinoxalines from halogenoquinoxalines (Section 4.4.1) the conversion of the thiocyanatoquinoxalines into alkoxyquinoxalines (Section 4.4.1), into quinoxalinethiones (Section... 

In addition to this, asymmetric 1,3-dipolar cyclization reactions of nitrones with olefins,40 41 catalytic enantioselective cyanation of aldehydes,42 catalytic enantioselective animation,43 and aza-Michael reactions44 have been reported, and high enantioselectivities are observed. 

Dipolar cycloaddition reactions, of nitrones to olefins, 46, 97 of 3-phenylsydnone, 46, 98 Dispiro[5.1.5.1]tetradecane-7,14-dione, photolysis to cyclohexylidene-cyclohexane, 47, 34 preparation from cyclohexanecarbonyl chloride and triethylamine, 47, 34 Displacement of bromine from 1-bromo-2-fluoroheptane to give 2-fluoro-heptyl acetate, 46, 37 N,N -Disubstituted formamidines from triethyl orthoformate and primary amines, 46, 41 N,N-Disubstituted thioureas from secondary amines and silicon tetra-isothiocyanate, 45, 69 N,N-Disubstituted ureas from secondary amines and silicon tetraiso-cyanate, 45, 69... 

Scheme 6.2 Cyanation of nitrones utilizing TMSCN as cyanide source and catalyst 9 yields in parentheses refer to uncatalyzed reactions.

Takemoto et al. disclosed the catalytic cyanation of nitrones promoted by a diaryl thiourea [70]. Semicatalytic amount of thiourea was employed to activate the nitrone by hydrogen bonding. 

The various classes of compounds featuring carbon-nitrogen multiple bonds that are substrates for organometallic addition comprise azomethines, immonium ions, nitrones, hydrazones, oxime ethers, amidinesimidoyl halides, nitriles, isonitriles, and cyanates. Dicyclohexylcarbodiimide is omitted here because it has been included in the carbonyl section (p.l 16) side by side with isocyanates and isothiocycanates. 

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