title: Experimental and DFT studies on competitive heterocyclic rearrangements. 3. A cascade isoxazole-1,2,4-oxadiazole-oxazole rearrangement.
abstract: The thermal rearrangements of 3-acylamino-5-methylisoxazoles 1 have been investigated under basic and neutral conditions and interpreted with the support of computational data. The density functional theory (DFT) study on the competitive routes available for the base-catalyzed thermal rearrangement of isoxazoles 1 showed that the Boulton-Katritzky (BK) rearrangement, producing the less stable 3-acetonyl-1,2,4-oxadiazoles 5, is a much more favored process than either the migration-nucleophilic attack-cyclization (MNAC) or the ring contraction-ring expansion (RCRE). In turn, an increase in reaction temperature will promote the MNAC of oxadiazoles 5, producing the more stable 2-acylaminooxazoles 8. The thermal rearrangement of 3-acylaminoisoxazoles 1 into oxazoles 8 can therefore be interpreted in terms of a cascade BK-MNAC rearrangement involving 3-acetonyl-1,2,4-oxadiazoles 5 as ancillary intermediates.
authors.affiliation: Dipartimento di Chimica Organica E. Paterno, Universita degli Studi di Palermo, Viale delle Scienze, Parco d'Orleans II, Edificio 17, I-90128 Palermo, Italy. pace@unipa.it
authors.forename: Andrea
authors.initials: A
authors.lastname: Pace
authors.forename: Paola
authors.initials: P
authors.lastname: Pierro
authors.forename: Silvestre
authors.initials: S
authors.lastname: Buscemi
authors.forename: Nicolò
authors.initials: N
authors.lastname: Vivona
authors.forename: Giampaolo
authors.initials: G
authors.lastname: Barone
mesh_terms: D003198:Computer Simulation; D003500:Cyclization; D008956:Models, Chemical; D015394:Molecular Structure; D010080:Oxazoles / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism; D013696:Temperature
chemical_list: D010080:Oxazoles