2,1-Bensoidoxazoles [anthranils]. Synthesis and opening of the isoxazole ring (review)
The present review covers the literature on the synthesis of 2,l-benzoisoxazoles (anthranils) (I), and reactions of this bicyclic system which involve opening of the isoxazole ring. Since a detailed and satisfactorily full review of the chemistry of 2, l-benzoisoxazoles was published in 1967 [96], the main thrust of the present review is to cover the literature of the last twenty years. It has nevertheless been necessary to include earlier publications, especially when these deal with general methods of synthesis of anthranils. t i. Synthesis of 2~l-Benzisoxazoles
Mechanism of the conversion of 2-nitrobenzyl systems into 2,1-benzisoxazoles
2-Nitrophenyl derivatives are converted into 2,1-benzisoxazoles via an intermediate which arises from an internal oxidation–reduction reaction; subsequent loss of water or ROH gives the benzisoxazole. The initial step is addition of an oxygen atom from the o-nitro-group to the α-carbon.
Neighbouring-group participation in pyrolysis of aryl azides
Kinetic studies of the pyrolysis of a series of substituted phenyl azides in decalin or di-n-butyl phthalate solutions have revealed substantial anchimeric assistance when a phenylazo-, nitro-, acetyl, or benzoyl group is the ortho-substituent. Eact Values for these four azides are respectively 22·4, 26·2, 25·8, and 27·2 kcal. mole–1, while for 4-nitrophenyl azide, it is 40·6. Corresponding 10–11A values are 3·0, 19, 5·8, 5·3, and 690,000. Driving-force values are calculated, and constitute the first set of quantitative data available on neighbouring-group abilities in reactions involving concerted π-bond reorganization. 
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 Values for 4-methyl-, 3-methyl-, and 6-methyl-2-nitrophenyl azide are 27·3, 29·0, and 28·8 kcal. mole–1, with corresponding 10–11A values of 42, 44, and 10. These results demonstrate the requirement that the azido- and nitro-groups both lie in the plane of the aromatic ring for ready cyclization.