Synfacts 2010(7): 0761-0761  
DOI: 10.1055/s-0029-1220137
Synthesis of Heterocycles
© Georg Thieme Verlag Stuttgart ˙ New York

Synthesis of 2,3-Dihydroisoxazoles from Enynes and Hydroxylamines

Contributor(s): Victor Snieckus, Cédric Schneider
X. Yu, B. Du, K. Wang, J. Zhang*
East China Normal University, Shanghai, P. R. of China
Further Information

Publication History

Publication Date:
22 June 2010 (online)

Significance

Reported is a rapid, metal-free, and regioselective synthesis of highly substituted 2,3-dihydroisoxazoles 3 via a reaction of hydroxyl­amines 2 with electron-deficient 1,3-conjugated enynes 1. The optimized conditions involve the use of catalytic Et3N as base. The scope of this ­reaction has been examined with different electron-deficient 1,3-conjugate enynes 1 and various substituted hydroxylamines 2 providing the products 3 regioselectively in moderate to good yields. Indeed, several EWGs on the electron-deficient 1,3-conjugated enynes (aldehyde, ketone, amide, and ester) and substituents on the alkene or alkyne moiety (R¹ = aryl, alkyl, styryl or ester group; R² = aryl or alkyl group) are tolerated. However, the reaction of the enones 4 with different hydroxyl-amines 2 under the same conditions produced the novel β-amino enone 5 rather than the expected products. A plausible, although unsubstantiated mechanism was proposed for the formation of the enone 5. The structures of products 3 and 5 were confirmed by single crystal X-ray analysis.