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In 1898, Lowry84 observed that a-nitrocamphor (81) under Nef conditions did not give the expected a-diketone, but instead a compound to which he assigned, with little evidence, the oximino anhydride structure (85). This structure was recently corrected by Larson and Wat85 to the /V-hydroxyimide (84).
The sequence (81 -> 84) has been proposed85,86 to account for this process which involves decomposition of the àñã-nitro anion by strong acid. The à-carbonyl group presumably stabilizes the aci-salt and thus could be responsible for inhibiting the normal Nef reaction. A similar transformation has been observed87 in the case of a 16-nitro-17-oxo steroid.
Ò. M. Lowry, J. Chem. Soc. p. 986 (1898).
85 H. O. Larson and E. K. W. Wat, J. Am. Chem. Soc. 85, 827 (1963).
86 I). St. C. Black, J. Chem. Educ. Submitted for publication (1968).
87 A. Hassner and J. Larkin, J. Am. Chem. Soc. 85, 2181 (1963).
Breslow and co-workers88 discovered the thermal ring expansion of the nitrobutenone (86) to the iV-hydroxymaleimide (88) which may be mechanistically similar to the abnormal Nef reaction of a-nitro-camphor. Breslow postulated the Æ-hydroxyoxaziran intermediate
O- "° <87>
(87), but suggested that acyl migration to oxygen would form the oximinoanhydride, which could then be converted to the product. Such oxaziran decomposition would give rise to the Lowry structure in the case of a-nitrocamphor, and it seems more reasonable to postulate acyl migration to nitrogen, a process which would directly give the AT-hydroxyimide (88). This proposal is consistent with the known rearrangements89,90 of oxaziranes.
It is possible that these rearrangements are quite general, but so far, this generality has not been established.
In a study of the nitrosation of camphor-3-glyoxylic acid (89), Chorley and Lapworth91 isolated a compound whose structure (90) has recently been clarified by Hatfield and Huntsman.92 Decarboxylation and ring expansion occur and the reaction is rationalized in the sequence 89 -> 90. The buttressing effect of a methyl group on
88 R. Breslow, Ï. Kivelevich, M. J. Mitchell, W. Fabian, and K. Wendel, J. Am. Chem. Soc. 87, 5132 (1965).
89 W. D. Emmons, in “Hcterocyclic Compounds with Three- and Four-membered Rings” (A. Weissberger, ed.), Pt. I, p. 624. Wiley (Interscience), New York, 1964.
90 E. Schmitz, Advan. Heterocyclic Chem. 2, 85 (1963).
91 P. Chorley and A. Lapworth, J. Chem. Soc. 117, 728 (1920).
92 L. D. Hatfield and W. T). Huntsman, J. Org. Chem. 32, 1800 (1967).
ÍçÑ-Õ/ í3 ñ÷/ó
/ > / ÷>-îí >
(89) COCOaH coco2h
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the endomethylene bridge appears to be important, as /S-santenone-3-glyoxylic acid (91) behaved similarly, whereas the a-isomer (92) and norcamphor-3-glyoxylic acid (93) did not yield hydroxamic acids. A similar kind of rearrangement occurs93 during nitrosation of
93 E. J. Moriconi, F. J. Creegan, Ñ. K. Donovan, and F. A. Spano, J. Org. Chem. 28, 2215 (1963).
2-alkyl- 1-indanones (94) and the corresponding hydroxyisocarbo-styrils (95) are obtained. Moriconi and Creegan94 have studied this
conversion extensively because of its synthetic utility. It is noteworthy that the Beckmann rearrangement of 1-indanonc oxime95 and the Schmidt reaction on l-indanone9e lead predominantly to the aryl migration product, 3,4-dihydrocarbostyril (96). In general, t-butyl
nitrite was used for the nitrosation of indanones and the rearrangement was found to occur in both acidic and basic conditions. Moriconi and Creegan proposed mechanistic sequences involving ring cleavage followed by recyclization of an oximinocarboxylic acid derivative such as 97.
A further type of nitro-group rearrangement gives rise to a cyclic hydroxamic ether. Noland et al.97 describe the action of cold, dilute sulfuric acid on the sodium salt of 5-nitronorbornene (98), which results in conversion to the oxazinone (101). This complex rearrangement is rationalized by the sequence 98 -»¦ 101 involving intermediate formation of the nitrile oxide (99) and the hydroxamic acid (100).
Robinson and co-workers98, "have studied the photorearrangement of steroidal 17-nitrites (102) to cyclic hydroxamic acids (103) in good
94 E. J. Moriconi and F. J. Creegan, J. Org. Chem. 31, 2090 (1966).
95 F. S. Kipping, J. Chem. Soc. 65, 480 (1894).
98 L. H. Briggs and G. C. De Ath, J. Chem. Soc. p. 456 (1937).
97 W. E. Noland, J. H. Cooley, and P. A. McVeigh, J. Am. Chem. Soc. 81, 1209 (1959).