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. VI. Identification of Neighbouring Group Effects in Pyrolysis of Azidopyridines and Azidoquinolines

1985 ◽  
Vol 38 (7) ◽  
pp. 1045 ◽  
Author(s):  
LK Dyall ◽  
WM Wah
Keyword(s):  
Nitro Group ◽  
Kinetic Studies ◽  
Anomalous Behaviour ◽  
Aryl Azides ◽  
Group Participation ◽  
Neighbouring Group Participation ◽  
Group 3 ◽  
High Degree ◽  
Group Effects

Although there are literature reports of anomalous behaviour on pyrolysis of ortho-nitroazido-pyridines and ortho-nitroazidoquinolines, we find that these compounds cyclize to the expected furazan 1-oxides in near-quantitative yields, and with a high degree of neighbouring group participation by the nitro group. Kinetic studies in decalin solution reveal the following rate enhancements by the ortho-nitro group: 3-azido-2-nitropyridine, 466 at least; 4-azido-3-nitropyridine, 5400; 4-azido-3,5-dinitropyridine, 640; 4-azido-3-nitroquinoline, 82.4; 5-azido-6-nitroquinoline, 27.6; 2-nitro-1-azidonaphthalene, 12.7. The unstable furazan oxide, [1,2,5] oxa-diazolo [3,4-c]pyridine 1-oxide, has now been characterized. [1,2,5] Oxadiazolo [3,4-b]pyridine 1-oxide decomposed in decalin at 145° to give products indicative of a nitrene intermediate.

Pyrolysis of Aryl Azides. XI. Enhanced Neighboring Group Effects of Carbonyl in a Locked Conformation

1992 ◽  
Vol 45 (12) ◽  
pp. 1991 ◽  
Author(s):  
LK Dyall ◽  
JA Ferguson
Keyword(s):  
Transition State ◽  
Nitrogen Loss ◽  
Bond Formation ◽  
Carbonyl Oxygen ◽  
Oxidative Cyclization ◽  
Nitrobenzene Solution ◽  
Aryl Azides ◽  
Neighboring Group ◽  
Neighbouring Group Participation ◽  
Cyclic Product

Rates of pyrolysis in nitrobenzene solution have been measured for 1-azido-9H-fluoren-9- one, 1-azido-9H-xanthen-9-one, 1-azidoacridin-9(10H)-one and 1-azidoanthracene-9,1O-dione; relative to azidobenzene at 120� these were respectively 5.68, 1750, 5090 and 18400. The lack of neighbouring group participation for the first azide is related to the large distance between carbonyl oxygen and the inner azido nitrogen atom, and the data argue against a published proposal that the transition state is stabilized by electrostatic attraction. In the remaining azides, the 'locked conformation' leads to much larger neighbouring group assistance than is observed for freely rotating ortho groups such as benzoyl (krel79). Only the last azide yields an isoxazole on pyrolysis , the second and third ones providing the first reported examples of neighbouring -group-assisted pyrolysis in which no cyclic product is obtained. These results are interpreted in terms of an electrocyclic mechanism in which the transition state is early and N---0 bond formation is less advanced than other changes in bonds. Much of the rate enhancement is attributed to an electron distribution which favours nitrogen loss. 1-Aminoanthracen-9(10H)-one, 1-amino-9H-fluoren-9-one and 1-amino-9H-xanthen-9-one do not yield the corresponding isoxazoles when oxidative cyclization is attempted.

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).

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.

scholarly journals Neighbouring Group Participation in the Methanolysis of a Vicinal Diepoxide

1999 ◽  
Vol 23 (6) ◽  
pp. 356-357
Author(s):  
James R. Hanson ◽  
Peter B. Hitchcock ◽  
Ismail Kiran
Keyword(s):  
Hydroxy Group ◽  
Group Participation ◽  
Neighbouring Group Participation

The tetracyanoethylene catalysed methanolysis of 17β-acetoxy-4β,5β:6α,7α-diepoxyandrostane afforded 17β-acetoxy-4α,7α-oxido-5β-hydroxy-6β-methoxyandrostane in which the methanolysis product of the 6α,7α-epoxide has participated in the cleavage of the 4β,5β-epoxide; the reaction is modified however by an adjacent 3β-hydroxy group.

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