Intramolecular carbene-type 1,1-cycloaddition by nitrile imines

The electronic structure of nitrilimine: absence of the carbenic form

“…Those authors claimed that the carbenic behaviour of nitrilimines is operating in the case of N-(2-vinylphenyl)-substituted nitrilimines, which cyclise to 1,2benzodiazepine and/or cyclopropa[c]cinnolines. 6 However, it has been demonstrated that the mechanism of these transformations involves a 1,7-electrocyclic reaction as the key step 7 and ''does not necessitate carbenic reactivity''. 8 Furthermore, scrupulous searches for azacarbene-derived products in the reaction between C-methoxycarbonyl-N-aryl-nitrilimines and allylic 9 or homoallylic 10 alcohols did not give any positive result, since only the usual pyrazoles due to the [3 + 2] cycloaddition were found in the reaction mixtures together with trivial side-products.…”

“…The geometry of singlet ground-state HCNNH was optimised at the CASSCF (8,6)/cc-pVTZ level and characterised by harmonic analysis. All p-bonding and non-bonding electrons are active so that we are confident that the wavefunction has proper variational freedom.…”

Synthesis of 2‐pyrazolines by the reactions of α,β‐unsaturated aldehydes, ketones, and esters with diazoalkanes, nitrile imines, and hydrazines

“…The synthesis of tricyclic 2-pyrazolines by an intramolecular 1,3-dipolar cycloaddition of nitrile imines is well documented in the literature [64][65][66][67][68][69][70][71][72][73][74][75][76] The structure and stereochemistry of compounds 74 have been elucidated by nmr spectroscopic measurements. These spectroscopic investigations revealed a regioselective and diastereoselective ring formation.…”

1,3,4-Thiadiazoles of pharmacological interest: Recent trends in their synthesis via tandem 1,3-dipolar cycloaddition: Review

“…Several convenient methods have been reported for the generation of nitrilimines [25–39] . These include (i) thermolysis of either 2,5-disubstituted tetrazoles 1 , 1,3,4-oxadiazol-5-ones 2 or 1,2,3,4-oxathiadiazol-2-oxides 3 (ii) base treatment of either hydrazonoyl halides 4 , α-nitroaldehyde hydrazones 5 or N-hydrazonoyl pyridinium salts 6 (iii) oxidation of aldehyde hydrazones 7 with lead tetracetate or ferric chloride and (iv) treatment of acid hydrazides 8 with triphenylphosphine in acetonitrile ( Chart 1 ).…”