Synthesis of 4-isoxazolines
Intramolecular cyclizations of propargylic N-hydroxylamines provide 4-isoxazolines rapidly at room temperature in the presence of 5 mol % (PPh3)AuCl/5 mol % AgOTf or 5 mol % (PPh3)AuNTf2. This process offers high yields, short reaction times, and mild reaction conditions.
B. Chandrasekhar, S. Ahn, J.-S. Ryu, J. Org. Chem., 2016, 81, 6740-6749.
The combination of ZnI2 and DMAP catalyzes a mild cyclization reaction of propargylic N-hydroxylamines to 2,3,5-trisubstituted 2,3-dihydroisoxazoles.
P. Aschwanden, D. E. Frantz, E. M. Carreira, Org. Lett., 2000, 2, 2331-2333.
Visible-light photoredox catalysis enables a green method for [3 + 2] cycloaddition of oxaziridines with alkynes to form 4-isoxazolines in good yields. This atom-economical reaction tolerates various functional groups. Moreover, the cyclization products can be conveniently converted into tetrasubstituted allylic alcohols and enamines.
G. S. Jang, J. Lee, J. Seo, S. K. Woo, Org. Lett., 2017, 19, 6448-6451.
An efficient cascade reaction of diethyl 2-(ethoxymethylene)malonate, different hydroxylamines and various amines provides ethyl 3-amino-5-oxoisoxazolidine-4-carboxylate derivatives, which are expected to be important in organic synthesis and medicinal chemistry.
R. Li, Q. Wei, X. Wang, Z. Ge, R. Li, Synthesis, 2017, 49, 4341-4349.