Neighbouring carboxy-group catalysis of ring opening of 3,1-benzoxazin-4-ones
- 1 January 1978
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 3,p. 208-212
- https://doi.org/10.1039/p29780000208
Abstract
Efficient intramolecular catalysis of the hydrolysis of 2-methyl-3,1-benzoxazin-4-ones to N-acetylanthranilic acids by a neighbouring carboxy-group [as in (6)] is demonstrated. The 8-carboxy-compound (6) reacts 250-fold faster than the 6-carboxy-isomer (7) at pH 6. A mechanism involving the 8-carboxy-group as an internal general acid catalyst is proposed. The 5-carboxy-isomer (9) does not show enhanced reactivity but, consistent with attack of the nucleophile at the 4-position of the benzoxazinone, hydroxide ion catalysed hydrolysis is actually depressed by the presence of the CO2 – group in this position. The anhydride (13)(formed by reaction of 3-aminophthalic acid with acetic anhydride) is hydrolysed directly (by H2O or HO– attack) at pH < 10; however at pH > 10 a preliminary rearrangement of the anhydride (13) to the benzoxazine (9) occurs.Keywords
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