Steric Effects in the Base-Catalyzed Cyclization of 1-[2-(Methoxycarbonyl)phenyl]-3-(2-substituted Phenyl)triazenes

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Title:Steric Effects in the Base-Catalyzed Cyclization of 1-[2-(Methoxycarbonyl)phenyl]-3-(2-substituted Phenyl)triazenes
Creators:
Ludwig, Miroslav
Bauerová, Ingrid
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 63, 12, pp. 2075-2084
Uncontrolled Keywords:Steric effect, Substituent effect, Reaction kinetics, Base catalyzed cyclization, Triazenes

Abstract

Eleven model 1-[2-(methoxycarbonyl)phenyl]-3-(2-substituted phenyl)triazenes were synthesized and their cyclization kinetics examined in aqueous-methanolic buffer solutions (51 wt.% methanol) at various pH values. 3(2-Substituted phenyl)benzo[<i>d</i>][1,2,3]triazin-4(3<i>H</i>)-ones were identified as the cyclization products. The log <i>k</i><sub>obs </sub><i>vs </i>pH plot was linear with a slope of unity. Investigation of the steric and electronic effects of substituents in the <i>ortho</i> position revealed that substituents at the ring which is bonded to the N(3) nitrogen affect the cyclization rate through their steric effect only, while their electronic effects are statistically insignificant. This fact was explained in terms of the ring being tilted from the plane in which the remaining part of the conjugate base anion of the model substrate lies. The assumed and confirmed B<sub>Ac</sub>2 mechanism involving specific base catalysis begins by deprotonation of the triazene giving rise to the conjugate base, continues with formation of a tetrahedral intermediate, and ends with elimination of the methanolate ion. Other mechanisms, such as the elimination-addition mechanism <i>via </i>a ketene intermediate or the mechanism involving general base catalysis, are unlikely.

Title:Steric Effects in the Base-Catalyzed Cyclization of 1-[2-(Methoxycarbonyl)phenyl]-3-(2-substituted Phenyl)triazenes
Creators:
Ludwig, Miroslav
Bauerová, Ingrid
Uncontrolled Keywords:Steric effect, Substituent effect, Reaction kinetics, Base catalyzed cyclization, Triazenes
Divisions:Life and Chemical Sciences > Institute of Organic Chemistry and Biochemistry > Collection of Czechoslovak Chemical Communications
Journal or Publication Title:Collection of Czechoslovak Chemical Communications
Volume:63
Number:12
Page Range:pp. 2075-2084
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc19982075UNSPECIFIED
ID Code:1446
Item Type:Article
Deposited On:06 Feb 2009 17:09
Last Modified:06 Feb 2009 16:09

Citation

Ludwig, Miroslav; Bauerová, Ingrid (1998) Steric Effects in the Base-Catalyzed Cyclization of 1-[2-(Methoxycarbonyl)phenyl]-3-(2-substituted Phenyl)triazenes. Collection of Czechoslovak Chemical Communications, 63 (12). pp. 2075-2084. ISSN 0010-0765

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