The Lifetime and Reactivity of Singlet Tetrachloropyridyl-4-nitrene

The principal direction in the photolytic decomposition of 4-azidotetrachloropyridine in methylene chloride solution involves the intermediate formation of singlet tetrachloropyridyl-4-nitrene, the lifetime of which amounts to 50 nsec. The nitrene reacts readily with the pyridine (k _pyr = 2.67·10⁷ mole^-1·sec^-1) with the formation of the corresponding pyridinium ylide, which has a characteristic absorption band in the UV spectrum with a maximum at 406 nm.     

Selective Thermolysis of Azide Groups in 2,4,6-Triazidopyridines

When refluxed in 1,4-dichlorobenzene, the compound 2,4,6-triazido-3,5-dichloropyridine and its 3,5-dicyano derivative undergo selective thermolysis of the -azide groups, forming the corresponding 4-amino-2,6-diazidopyridines in high yields. According to quantum-chemical calculations, the selectivity of thermolysis of the -azide groups in triazides is due to the weaker bonding interactions between the N₍₎ and N₍₎ atoms in these azide groups.     

13C and 15N NMR spectra of high‐energy polyazidocyanopyridines

¹³C and ¹⁵N NMR spectra of high‐energy 2,4,6‐triazidopyridine‐3,5‐dicarbonitrile, 2,3,5,6‐tetraazidopyridine‐4‐carbonitrile and 3,4,5,6‐tetraazidopyridine‐2‐carbonitrile are reported. The assignment of signals in the spectra was performed on the basis of density functional theory calculations. The molecular geometries were optimized using the M06‐2X functional with the 6‐311+G(d,p) basis set. The magnetic shielding tensors were calculated by the gauge‐independent atomic orbital method with the Tao–Perdew–Staroverov–Scuseria hybrid functional known as TPSSh. In all the calculations, a polarizable continuum model was used to simulate solvent effects. This approach provided accurate predictions of the ¹³C and ¹⁵N chemical shifts for all the three compounds despite complications arising due to non‐coplanar arrangement of the azido groups in the molecules. It was found that the ¹⁵N chemical shifts of the N_α atoms in the azido groups of 2,4,6‐triazidopyridines correlate with the ¹³C chemical shifts of the carbon atoms attached to these azido groups. Copyright © 2016 John Wiley & Sons, Ltd.     

Regioselective Cycloaddition of the Dimethyl Ester of Acetylenedicarboxylic Acid to 2,4,6-Triazidopyridines

2,4,6-Triazido-3,5-dichloropyridine was obtained in the reaction of pentachloropyridine with sodium azide. At room temperature, this azide reacts regioslectively with norbornene at the -azide group to give the corresponding 4-(3-azatricyclo[3.2.1.0]octanyl)-2,6-diazidopyridine in 88% yield. The cycloaddition of the dimethyl ester of acetylenedicarboxylic acid to this triazide proceeds at the azide groups at C₍₂₎ and C₍₆₎ in the pyridine ring to give 4-azido-2,6-di(4',5'-dimethoxycarbonyl)-1H-1,2,3-triazolopyridine. The analogous reaction of 2,4,6-triazido-3,5-dicyanopyridine with the dimethyl ester of acetylenedicarboxylic acid stops at the formation of 2,4-diazido-6-(4',5'-dimethoxycarbonyl)-1H-1,2,3-triazolopyridine. In contrast to reactions with electron-rich dipolarophiles, the cycloaddition of electron-deficient dipolarophiles to 2,4,6-triazidopyridines proceeds with thermodynamic control primarily a! t the azide groups bearing the highest orbital density in the HOMO.     

15N NMR spectra and reactivity of 2,4,6‐triazidopyridines, 2,4,6‐triazidopyrimidine and 2,4,6‐triazido‐s‐triazine

2,4,6‐Triazido‐s‐triazine, 2,4,6‐triazidopyrimidine and six different 2,4,6‐triazidopyridines were studied by ¹⁵N NMR spectroscopy. The assignment of signals in the spectra was performed using the gauge‐independent atomic orbital (GIAO)–Tao‐Perdew‐Staroverov‐Scuseria exchange‐correlation functional (TPSS)h/6‐311+G(d,p) calculations on the M06‐2X/6‐311+G(d,p) optimized molecular geometries. The Truhlar and coworkers' continuum solvation model called SMD was applied to treat solvent effects. With this approach, the root mean square error in estimations of the ¹⁵N chemical shifts for the azido groups was just 1.9 ppm. It was shown that the different reactivity of the α‐ and γ‐azido groups in pyridines correlates well with the chemical shifts of the N_α signals of these groups. Of two nonequivalent azido groups of azines, the azido group with the most shielded N_α signal is the most electron‐deficient and reactive toward electron‐rich reagents. By contrast, the azido group of azines with the most deshielded N_α signal is the most reactive toward electron‐poor reagents. Copyright © 2013 John Wiley & Sons, Ltd.