Reactions of cyclopropanone acetals with alkyl azides: carbonyl addition versus ring-opening pathways.
The Lewis acid-mediated reactions of substituted cyclopropanone acetals with alkyl azides were found to strongly depend on the structure of the ketone component. When cyclopropanone acetal was treated with alkyl azides, N-substituted 2-azetidinones and ethyl carbamate products were obtained, arising from azide addition to the carbonyl, followed by ring expansion or rearrangement, respectively. When 2,2-dimethylcyclopropanone acetals were reacted with azides in the presence of BF3.OEt2, the products obtained were alpha-amino-alpha'-diazomethyl ketones, which arose from C2-C3 bond cleavage of the corresponding cyclopropanone, giving oxyallyl cations that were captured by azides. Aryl-substituted cyclopropanone acetals, when subjected to these conditions, afforded [1,2,3]oxaborazoles exclusively, which were also the result of C2-C3 bond rupture, azide capture, and then loss of nitrogen. In the reactions of n-hexyl-substituted cyclopropanone acetals with alkyl azides, a mixture of 2-azetidinones and regioisomeric [1,2,3]oxaborazoles was obtained. The reasons for the different behavior of the various systems are discussed.
Grecian
Scott
S
Department of Medicinal Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, KS 66045-7582, USA.
Desai
Pankaj
P
Mossman
Craig
C
Poutsma
Jennifer L
JL
Aubé
Jeffrey
J
D000080:Acetals / Q000737:chemistry*; D001386:Azides / Q000737:chemistry*; D003521:Cyclopropanes / Q000737:chemistry*; D007659:Ketones / Q000138:chemical synthesis / Q000737:chemistry; D008956:Models, Chemical; D015394:Molecular Structure; D013237:Stereoisomerism
D000080:Acetals; D001386:Azides; D003521:Cyclopropanes; D007659:Ketones