Some synthetic applications of the reaction of reductive opening of the isoxazole ring

Studies on the catalytic hydrogenation of Baylis–Hillman derivatives of substituted isoxazolecarbaldehydes. Unusual retention of isoxazole ring during Pd–C-promoted hydrogenation of Baylis–Hillman adducts

“…[23][24][25] In a similar observation Chimichi et al recently reported the synthesis of substituted 3(2H)-furanones through appropriately substituted a 0 -hydroxy-1,3-diketones utilizing isoxazoles as the starting substrate. As part of our objectives to demonstrate the synthetic utility of the enaminones synthesized during this study, compounds 4a-b, 5b and 19a-b, d were subjected to acid-promoted cyclizationdehydration reaction.…”

Preparation of long‐chain β‐enaminones and β‐diketones from long‐chain 3,5‐disubstituted isoxazole compounds

“…Various methods based on Raney nickel (6,7), samarium diiodide (8), and molybdenum hexacarbonyl (9) have been used to convert the isoxazole ring into β-enaminones via cleavage of the isoxazole's weak N-O bond. Initially, we tried using the procedure based on Mo(CO) 6 (9) to open the isoxazole ring of these compounds, but our initial attempts proved unsuccessful. Therefore, this approach was abandoned in favor of the procedures based upon Raney nickel (6,7).…”

“…The isoxazole ring also serves as a versatile synthetic intermediate that can undergo a variety of chemical transformations useful to construct many types of interesting molecules (5). The isoxazole ring's weak N-O bond (approximately 52 kcal/mol) is readily opened under mild conditions to give β-enaminones (6)(7)(8)(9). The βenaminone functionality has found widespread use in synthesis (10) and also has been shown to display interesting pharmacological properties (11,12).…”

Five‐Membered Heterocycles: 1,2‐Azoles. Part 2. Isoxazoles and Isothiazoles

“…Starting from bisnitrile oxides the reaction with alkynes leads to 3,3 0 -linkage of the isoxazole rings whereas the cycloaddition of nitrile oxides with diynes produces a 5,5 0 -linkage [6,[161][162][163][164][165]. The reaction of oxime dianions with carbonyl compounds (e.g., esters, amides or aroyl chlorides) is an alternative regioselective method for the construction of the isoxazole ring (Scheme 9.15).…”