Studies on heterocyclic chemistry. III. Thermally induced skeletal rearrangement of 5-alkoxyisoxazoles into alkyl 1-azirine-3-carboxylates

Photochemical transformations of small ring heterocyclic compounds. 70. Thermal and photochemical valence isomerizations of 4-carbonyl-substituted isoxazoles

“…It is interesting to note that 5-alkoxyisoxazoles have been reported to undergo a facile thermally induced skeletal rearrangement to alkyl-1azirine-3-carboxylates. 32 This rearrangement provides good analogy for the ring contraction step of the proposed sequence. The literature also contains several references dealing with the thermal rearrangement of 4-isoxazolines.33-37 Most of the rearrangements observed with these systems can also be attributed to a ring contraction-ring expansion sequence.…”

“…The aqueous suspension was extracted with ether and the ethereal layer was dried over magnesium sulfate. Removal of the solvent left a white solid which was recrystallized from aqueous ethanol to give 1.07 g of the oxime of 3-phenyl-5-methyl-4-acetylisoxazole (32): mp 121-122°; ir (KBr) 3.00, 6.20, 6.80, 7.00, 7.60, 7.95, 8.70, 9.25, 9.65,9.81, 10.95, 12.70, 13.25, 13.65, and 14.20 µ; NMR (CDC13) 10.4 (broad s, 1 H), 7.3-7.5 (m, 5 ), 2.50 (s, 3 ), 1.90 (s, 3 H).…”

Valence tautomers of heterocyclic aromatic species

“…Fraction 1, a very minor constituent (<1%) of the reaction mixture, was characterized as the enedione (15) on the basis of the following data: ir (CC14) 3070 (w), 1684 (s), 1589 (s), and 868 cm-1 (s); nmr (CC14) 8.87, 8.83, 8.81 (singlets, 27 H), 3.48 (s, 1 H); uv (EtOH) (e) 300 sh (172). 237.5 nm (5200); mass spectrum (70 eV) mje (relative intensity) 252 (2), 196 (25), 195 (100), 181 (31), 180 (87), 165 (13), 138 (18), 111 (11), 109 (13), 95 (30), 67 (33), 57 (73), 55 (18), 43 (27), 42 (13), 41 (62), and 39 (25). Fraction 2, the major product (ca.…”

Studies on the intramolecular addition of vinyl nitrenes to olefins

“…Careful monitoring of the reaction showed that 22 was not converted 22 to 1 by a Cope rearrangement, as had been encountered with the closely related cyclopropene system.27 Subjection of azirine 27 to similar pyrolysis conditions gave 2-methyl-3-(l-methylallyl)indole (28) and 2,4-dimethyl-3phenylpyridine (29) as the major thermal products. The 27, R, = CH3:R. = H 28, R. = CH3;R2 = H 29 30, R, = H; R2 = CH3 31, R¡ = H; R3 = CH3 structure of indole 28 was verified by comparison with an authentic sample prepared from the reaction of 2-methylindole (26) with 3-chloro-l-butene. In this case there were no detectable quantities of a 3-aza-substituted bicyclohexene.…”

“…In this case there were no detectable quantities of a 3-aza-substituted bicyclohexene. Thermolysis of the closely related 2-(2-methylallyl)-3methyl-2-phenyl-2H-azirine (30) gave indole 31 (89%) as the only characterizable material. The structure of this material was verified by comparison with an authentic sample.…”