85796-88-9Relevant articles and documents
Formation of a cyclic tetrahedral intermediate by the addition of water to 2-methyl-4H-3,1-benzoxazine followed by ring opening to 2-aminobenzyl acetate and 2-acetylaminobenzyl alcohol; pH-dependence of rate of reaction and product ratio
Dixon, Wendy J.,Hibbert, Frank
, p. 1035 - 1041 (2007/10/03)
Kinetic studies have shown that addition of water to protonated 2-methyl-4H-3,1-benzoxazine occurs to give a cyclic tetrahedral carbonyl addition intermediate. At pH 7.5, the unprotonated intermediate collapses to give 2-acetylaminobenzyl alcohol. The former reaction is catalysed by buffer base but the latter is uncatalysed. At pH 9-12, reaction of hydroxide ion with protonated 2-methyl-4H-3,1-benzoxazine to give 2-acetylaminobenzyl alcohol becomes important, and at pH >12, the same product is formed by reaction of hydroxide ion with unprotonated 2-methyl-4H-3,1-benzoxazine.
Rearrangement of N-acyl-3,4-dihydro-1H-2,1-benzoxazines to 2-substituted-4H-3,1-benzoxazines through a retro-Diels-Alder extrusion of formaldehyde
Glover, Stephen A.,Jones, Katherine M.,McNee, Ian R.,Rowbottom, Colleen A.
, p. 1367 - 1376 (2007/10/03)
N-Acyl-3,4-dihydro-1H-2,1-benzoxazines (3) undergo a thermal decomposition involving loss of formaldehyde in a retro-Diels-Alder reaction. The resultant N-acylazaxylylenes? (4) undergo a 6π electrocyclisation to give 2-substituted-4H-3,1-benzoxazines (5) rather than a 4π electrocyclisation to give the N-acyl-1,2-dihydrobenzazetes (6). Compounds 5 have been fully characterised spectroscopically and their data is inconsistent with that reported previously by other workers for what are purported to be the same compounds. 2-Methyl-4H-3,1-benzoxazine (5b) and other 2-alkyl-substituted compounds undergo facile hydrolysis to o-aminobenzyl esters (9) which rearrange to the thermodynamically more stable o-hydroxymethylanilides (10). 2-Phenyl-4H-3,1-benzoxazine (5a) is relatively stable to hydrolysis but undergoes a novel photochemical ring opening (> 254 nm) to give the N-benzoylazaxylylene (12) which can be trapped with alcohols giving o′-alkoxymethylbenzanilides (11). In cyclohexanol at 160°C, the intermediate in the thermal rearrangement of 3a to 5a, N-benzoylazaxylylene (12), was trapped as o′-cyclohexyloxymethylbenzanilide (11b). The rearrangements in mesitylene are unimolecular with activation energies of 35, 37 and 42 kcal mol-1 ? for 3a; 3c and 3d, respectively. The extrusion and electrocyclisation reaction pathways for N-acetyl-3,4-dihydro-2,1- benzoxazine (3b) have been modelled using AM1 molecular orbital theory which predicts both a non-synchronous transition state for the retro-Diels-Alder reaction and the preferred mode of ring closure to be the 6π rather than the 4π electrocyclisation.
