Methyl Cyanoformate cycloadditions

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... 

If the C=N function is attached to an electron-withdrawing group, 1,3-dipolar cycloaddition with diazoalkanes occurs leading to 1,2,3-triazoles (5, 276). When diazomethane is used, the initially formed NH-triazole is not isolated due to a rapid subsequent NH deprotonation followed by N-methylation. Consequently, a mixture of the three Wmethyltriazoles is formed when methyl cyanoformate (71) (216) or trichloroacetonitrile (276) (217) is treated with excess diazomethane (Scheme 8.51). Huisgen and co-workers found that methyl diazoacetate reacts with TCNE by a 1,3-dipolar cycloaddition at the C=C bond and not, as published earlier by other authors, at one of the nitrile functions (72). 

A 1,4-dipolar cycloaddition between tetrahydropyrido[l,2-a]pyrimidi-none 114 (R = Me) and 4-methyl-l, 2,4-triazoline-3,5-dione 666gave stable adduct 667 in acetonitrile or in acetic acid at room temperature for 1 hour (Scheme 44) (85CB4567). When ethyl cyanoformate was used as dienophile in boiling toluene for 20 hours, ethyl 3-methyl-4-oxo-6,7,8,9-tetrahydro-4//-pyrido[ 1,2-a]pyrimidine-2-carboxylate 669 was obtained (86CB1445). Pyrido[l,2-a]pyrimidine-2-carboxylate 669 was formed from the initial adduct 668 by elimination of phenyl isocyanate. Reaction of tetrahydropyr-ido[l,2-a]pyrimidinone 114 (R = Me) with l-(diethylamino)-l-propyne in... 

Cycloadditions. Methyl and ethyl cyanoformate have been reported to undergo [4 + 2] cycloadditions, e.g. with cyclopentadienones and 2-alkyl-l-ethoxybuta-1,3-dienes to form pyridines (eq 21), and with cyclobutadienes to form Dewar pyridines (eq 22). Ethyl cyanoformate is also ein effeetive dipolarophile, undergoing 1,3-dipolar addition to azides (eq 23) and cyclic carbonyl ylides (eq 24). ... 

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