- The base-catalysed cyclisation of phenyl N-(2-hydroxybenzyl)-N-methylcarbamates is concerted
-
The kinetics of the cyclisation in aqueous solution of phenyl-(2-hydroxybenzyl) -N-methylcarbamates to 3-methyl-3,4-dihydrobenzol[e][1,3]oxazin-2-ones and phenolate ions fit the rate law: kobs = kc/(1 + [H3O+]/ ka) The values of kc and pKa fit Broonsted equations agains the pKa's of the corresponding free phenols but the system does not conform to the reactivity-selectiviy hypothesis. The values of the Broonsted parameters βY and βX vary as a function of Y and X according to the equations: βX = -0.179pKaHY + 0.87 βY = -0.179pKaHX + 2.30 The magnitude and sign of the Cordes-Thornton cross-interaction coefficient pXY(-0.179) rule out a stepwise mechanism involving a tetrahedral intermediate and is consistent with a concerted displacement mechanism. A similar concerted mechanism is proposed for the base-catalysed cyclisation of phenyl-N-(2-hydroxyphenyl)-N-methylcarbamate esters to benzoxazol-2-ones.
- Sterba, Vojeslav,Hrabik, Oldrich,Kavalek, Jaromir,Mindl, Jaromir,Williams, Andrew
-
p. 415 - 421
(2007/10/03)
-
- Cyclization of substituted phenyl N-(2-hydroxybenzyl)carbamates in aprotic solvents. Synthesis of 4H-1,3-benzoxazin-2(3H)-ones
-
The kinetics of cyclization of substituted phenyl N-(2-hydroxybenzyl)carbamates and their N-methyl analogs, prepared by the reaction of 2-(aminomethyl)phenols with substituted phenyl chloroformates, was studied in dioxane or toluene at the temperatures 110-180 °C. Electron-withdrawing substituents in the leaving phenoxy group strongly accelerate the rate of cyclization (ρ = 2.45 ± 0.15) while the substituents in the other ring have virtually no effect. The cyclization was catalyzed with triethylamine in toluene but not in dioxane. On the basis of these results, the most convenient method for preparation of substituted 4H-1,3-benzoxazin-2(3H)-ones was a one-hour reflux of substituted 4-nitrophenyl N-(2-hydroxybenzyl)carbamates in dioxane. Based on the influence of substituents, solvents (dioxane and toluene) and triethylamine, the reaction mechanism and structure of the transition state were proposed.
- Mindl, Jaromir,Hrabik, Oldrich,Sterba, Vojeslav,Kavalek, Jaromir
-
p. 1262 - 1272
(2007/10/03)
-
- 3,4-Dihydro-3-methyl-6-nitro-2H-1,3-benzoxazin-2-one, a Reagent for Labeling p-Nitrophenyl Esterases with a Chromophoric Reporter Group - Synthesis and Reaction with Chymotrypsin
-
We reported the synthesis of 3,4-dihydro-3-methyl-6-nitro-2H-1,3-benzoxazin-2-one (DMNB), a close structural anlogue of p-nitrophenyl dimethylcarbamate.DMNB is unstable in aqueous solution when exposed to light, but is stable in the dark.The compound reac
- Kitson, Trevor M.,Freeman, Graham H.
-
p. 354 - 365
(2007/10/02)
-