Pyrolysis of aryl azides. IV. Neighbouring group effects by ortho carbonyl groups

1977 ◽  
Vol 30 (12) ◽  
pp. 2669 ◽  
Author(s):  
LK Dyall
Keyword(s):  
Carbonyl Groups ◽  
Aryl Azides ◽  
Phenyl Azide ◽  
Sterically Hindered ◽  
Group Effects

The question of the mechanism by which ortho carbonyl groups enhance the rate of pyrolysis of aryl azides is examined. Rate measurements on sterically hindered 1-(2-azidophenyl)ethan-1-ones are consistent with the pericyclic mechanism proposed by Dyall and Kemp1 but not with the intramolecular 1,3-dipolar addition route put forward by Hall, Behr and Reed.2 A definitive test of mechanism is also provided by 1- azidoanthraquinone and 1-(2-azidophenyl)-2,2-dimethylpropan-1-for both of which the formation of a 1,3-dipolar adduct is precluded on steric grounds but the pericyclic process is not. At 393.2 K, these two azides pyrolyse 7385 and 61.7 times faster than phenyl azide, respectively.

Pyrolysis of aryl azides. II. Naphthyl azides

1972 ◽  
Vol 25 (3) ◽  
pp. 599 ◽  
Author(s):  
G Boshev ◽  
LK Dyall ◽  
PR Sadler
Keyword(s):  
Nitro Group ◽  
Steric Effect ◽  
Kinetic Studies ◽  
Oxidative Cyclization ◽  
Nitrobenzene Solution ◽  
Aryl Azides ◽  
Phenyl Azide ◽  
Group Participation ◽  
Neighbouring Group Participation ◽  
Group Effects

Kinetic studies of the pyrolyses of 1- and 2-naphthyl azides reveal neighbouring group participation by nitro and phenylazo substituents. The acceleration observed in 1-nitro-2-naphthyl azide, 1-phenylazo-2-naphthyl azide, and 2-nitro-1-naphthyl azide is 1730-, 211-, and 23.6-fold, respectively, in nitrobenzene solution at 120�. These effects are all smaller than that of the 2-nitro group in phenyl azide (3370-fold), which is ascribed to the steric effect of the peri hydrogen at C8 in naphthyl azides. The sizes of these neighbouring group effects correlate with the success of oxidative cyclization of ortho-substituted naphthylamines with (diacetoxyiodo)benzene.

Pyrolysis of Aryl Azides.X. Effects of Azide Concentration on Rate Constants and Product Yields

1990 ◽  
Vol 43 (6) ◽  
pp. 997 ◽  
Author(s):  
LK Dyall ◽  
PAS Smith
Keyword(s):  
Free Radical ◽  
Rate Constants ◽  
Aryl Azides ◽  
Radical Chain ◽  
Initial Concentration ◽  
Azo Compound ◽  
Product Yields ◽  
First Order ◽  
Induced Decomposition ◽  
Group Effects

First-order rate constants (k1) have been measured for pyrolysis of azidobenzenes in decalin solution, in the presence of a free-radical chain inhibitor to prevent any induced decomposition. The new values of k1 for the spontaneous unimolecular thermolysis are lower than previously reported ones, and require revision of published neighbouring group effects. Product yields ( azo compound and primary amine) vary with initial concentration of azide in ways which suggest the species responsible for induced decomposition is not triplet arylnitrene , but a solvent-derived free radical. There is no evidence for induced decomposition when nitrobenzene is the solvent. For aryl azides with no neighbouring group effects operating in their pyrolysis, the Arrhenius parameters Eact and ΔSactobey a precise linear relationship.

Pyrolysis of aryl azides. III. Steric and electronic effects upon reaction rate

1975 ◽  
Vol 28 (10) ◽  
pp. 2147 ◽  
Author(s):  
LK Dyall
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Reaction Rate ◽  
Steric Effects ◽  
Electronic Effects ◽  
Aryl Azides ◽  
Phenyl Azide ◽  
Methyl Group ◽  
First Order ◽  
Ortho Substituent

First-order rate constants have been measured for the pyrolysis of 15 phenyl azides in decalin solution. The rate for phenyl azide is increased only slightly by all para and many ortho substituents; in these cases Eact and ΔSact values are related linearly. ��� The very large rate increases when the ortho substituent is phenylazo, nitro, acetyl or benzoyl cannot be from steric or normal electronic effects and therefore identify a specific involvement of these groups in the transition state. This rate enhancement is reduced to scarcely significant levels by a 6-chloro or 6-methyl group in 2- nitrophenyl azide, but not by a 6-nitro group. These results raise doubts about recent claims1 to establish mechanism by measuring polar effects on rates of pyrolysis of azides in which steric effects might also operate.

[N,N′-Bis(2,6-diisopropylphenyl)acenaphthene-1,2-diimine-1κ2N,N′]heptacarbonyl-1κC,2κ3C,3κ3C-di-μ3-tellurido-triiiron(II)(2Fe—Fe)

2012 ◽  
Vol 68 (11) ◽  
pp. m320-m322 ◽  
Author(s):  
Dmitry A. Piryazev ◽  
Mikhail A. Ogienko ◽  
Alexander V. Virovets ◽  
Nikolay A. Pushkarevsky ◽  
Sergey N. Konchenko
Keyword(s):  
Electron Transfer ◽  
Title Complex ◽  
Cluster Core ◽  
Carbonyl Groups ◽  
Asymmetric Unit ◽  
Bond Lengths ◽  
Low Level ◽  
Redox Active ◽  
Sterically Hindered

The sterically hindered title complex, [Fe3Te2(C36H40N2)(CO)7], was obtained by substitution of two carbonyl groups in the [Fe3(μ3-Te)2(CO)9] cluster by the bulky redox-activeN,N′-bis(2,6-diisopropylphenyl)acenaphthene-1,2-diimine (dpp-BIAN) ligand. The asymmetric unit contains two molecules of the same geometry. The C=N bond lengths in dpp-BIAN indicate a rather low level of electron transfer from the cluster core to the dpp-BIAN ligand.

scholarly journals Further enhancement of the clickability of doubly sterically-hindered aryl azides by para-amino substitution

2018 ◽  
Vol 54 (96) ◽  
pp. 13499-13502 ◽  
Author(s):  
Suguru Yoshida ◽  
Junko Tanaka ◽  
Yoshitake Nishiyama ◽  
Yuki Hazama ◽  
Takeshi Matsushita ◽  
...  
Keyword(s):  
Amino Group ◽  
Aryl Azides ◽  
Sterically Hindered

Introduction of an amino group at the para position of doubly sterically-hindered aryl azides significantly enhances their clickability with cyclooctynes.

Exploiting the Facile Release of Trifluoroacetate for the α-Methylenation of the Sterically Hindered Carbonyl Groups on (+)-Sclareolide and (−)-Eburnamonine

2011 ◽  
Vol 76 (10) ◽  
pp. 3676-3683 ◽  
Author(s):  
Mark V. Riofski ◽  
Jinu P. John ◽  
Mary M. Zheng ◽  
Julia Kirshner ◽  
David A. Colby
Keyword(s):  
Carbonyl Groups ◽  
Sterically Hindered

Pyrolysis of Aryl Azides. XII. Mechanistic Implications of the Very Small Neighboring Group Effects Across the 2,3-Bond of 2-Azidonaphthalene

1994 ◽  
Vol 47 (6) ◽  
pp. 1031 ◽  
Author(s):  
LK Dyall ◽  
JA Ferguson
Keyword(s):  
Transition State ◽  
Dilute Solution ◽  
Nitrobenzene Solution ◽  
Aryl Azides ◽  
Neighboring Group ◽  
Spectroscopic Evidence ◽  
Infrared Spectroscopic ◽  
Group Effects

2-Azidonaphthalenes with nitro, acetyl, benzoyl and methoxycarbonyl substituents in the 3-position have been synthesized and then pyrolysed in nitrobenzene solution. At 120°, the rates (relative to 2-azidonaphthalene) are respectively 27.9, 24.8, 5.00 and 3.67. These very small neighbouring group effects are consistent with a transition state which has considerable quinonoid character. No evidence of cyclic products was obtained from the two azides with nitro and ester neighbouring groups. With the two azido ketones there was infrared spectroscopic evidence of clean cyclization in dilute solution, to form the corresponding naphth [2,3-c] isoxazole. Our attempts to isolate these two naphthisoxazoles led to decomposition, though 3-methylnaphth[2,3-c] isoxazole has been reported previously ( Friedrichsen and Kaschner 1977).

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