Photolysis of open-chain 1,2-diazidoalkenes: generation of 2-azido-2H-azirines, formyl cyanide, and formyl isocyanide

Copper-Mediated Synthesis of (E)-1-Azido and (Z)-1,2-Diazido Alkenes from 1-Alkene-1,2-diboronic Esters: An Approach to Mono- and 1,2-Di-(1,2,3-Triazolyl)-Alkenes and Fused Bis-(1,2,3-Triazolo)-Pyrazines

A stereoselective and convenient route has been demonstrated to access (Z)-1,2-diazido alkenes from the corresponding 1,2-diboronic esters via a copper-mediated reaction with sodium azide. Alternately, mono-functionalization was regioselectively carried out with trimethylsilyl azide as an azidation reactant. The in situ conversion of bis-azides to the corresponding bis-triazoles can be readily achieved in the presence of copper sulfate and sodium ascorbate, while the modification of the catalytic system opened a new convenient route to bis-triazolo-pyrazines, a new class of fused heterocycles.

Conformer-specific [1,2]H-tunnelling in captodatively-stabilized cyanohydroxycarbene (NC-C[combining umlaut]-OH)

We report the gas-phase preparation of cyanohydroxycarbene by high-vacuum flash pyrolysis of ethyl 2-cyano-2-oxoacetate and subsequent trapping of the pyrolysate in an inert argon matrix at 3 K. After irradiation of the matrix with green light for a few seconds singlet trans-cyanohydroxycarbene rearranges to its cis-conformer. Prolonged irradiation leads to the formation of cyanoformaldehyde and isomeric isocyanoformaldehyde. Cis- and trans-cyanohydroxycarbene were characterized by matching matrix IR and UV/Vis spectroscopic data with ab initio coupled cluster and TD-DFT computations. Trans-cyanohydroxycarbene undergoes a conformer-specific [1,2]H-tunnelling reaction through a 33.3 kcal mol-1 barrier (the highest penetrated barrier of all H-tunnelling reactions observed to date) to cyanoformaldehyde with a half-life of 23.5 ± 0.5 d; this is the longest half-life reported for an H-tunnelling process to date. During the tunnelling reaction the cis-conformer remains unchanged over the same period of time and the Curtin-Hammett principle does not apply. NIR irradiation of the O-H stretching overtone does not enhance the tunnelling rate via vibrational activation. Push-pull stabilisation of hydroxycarbenes through σ- and π-withdrawing groups therefore is even more stabilizing than push-push substitution.

Direct observation and characterisation of 3-azido-2H-azirines: postulated, but highly elusive intermediates

The title compounds, including the parent 3-azido-2H-azirine, were generated by low-temperature photolysis of the corresponding 1,1-diazidoethenes, and characterised not only by trapping reactions, but also by direct detection using NMR and in situ IR spectroscopy.

Chopping unfunctionalized carbon–carbon bonds: a new paradigm for the synthesis of organonitriles

Chopping of carbon–carbon bonds was very recently shown to be an efficient new strategy for the synthesis of organonitriles, as developed in this Highlight.

Cleavage of carbon-carbon triple bond: direct transformation of alkynes to nitriles

A new cleavage reaction of carbon-carbon triple bonds proceeds efficiently with NIS and TMSN3, giving the corresponding nitriles in moderate to good yields.