Silver-catalyzed synthesis of disubstituted isoxazoles by cyclization of alkynyl oxime ethers

One‐Pot Synthesis of 3,5‐Disubstituted Isoxazoles from Propargylic Alcohols through Propargylic N‐Hydroxylamines

“…(3‐Phenylisoxazol‐5‐yl)methanol (4g): 19 Viscous liquid. IR (KBr): $\tilde {\nu}$ = 3368, 2924, 1607, 1445, 1406, 1168, 1037, 768, 693 cm –1 .…”

Transition Metal-Mediated Synthesis of Monocyclic Aromatic Heterocycles

“…554 In 2011, the Ag(I)-catalyzed cycloisomerization of benzyl ethers of β-alkynyl oximes into isoxazoles was reported by Miyata. 555 …”

Cyclocondensation of Hydroxylamine with 1,3‐Bis(het)arylmonothio 1,3‐Diketones and 1,3‐Bis(het)aryl‐3‐(methylthio)‐2‐prop­enones: Synthesis of 3,5‐Bis(het)arylisoxazoles with Complementary Regioselectivity

“…Similarly, Larock9a,9b has described iodine‐catalysed electrophilic cyclization of O ‐methyloximes of acetylenic ketones to give 3,5‐substituted‐4‐iodooxazoles, which can be transformed further into 3,4,5‐substituted isoxazoles by palladium‐catalysed cross‐coupling 9b,9c. In parallel strategies, Miyata and co‐workers have developed a practical synthesis of 3,5‐disubstituted isoxazoles by silver‐catalysed cyclization of O ‐benzylalkynyloxime ethers,10a along with a gold‐catalysed domino reaction of O ‐allylalkynyloxime ethers involving cyclization and subsequent Claisen‐type rearrangement to give trisubstituted isoxazoles in a highly regioselective manner 10b. Other recently published methods include the iodocyclization of N ‐alkoxycarbonyl‐ O ‐propargylic hydroxylamines;11a a sequential iron‐ and palladium‐catalysed transformation of propargyl alcohols into N ‐protected propargylhydroxylamines, and their subsequent cyclization and coupling with various aryl iodides to give trisubstituted isoxazoles in a multistep one‐pot reaction;11b base‐catalysed cyclocondensation of activated nitromethylene compounds with dipolarophiles;3c,12a–12c zinc‐triflate‐catalysed aerobic cross‐dehydrogenative coupling (CDC) of alkynes with nitrones;13a hypervalent‐iodine‐induced cycloaddition of nitrile oxides to alkynes;13b–13d N ‐heterocyclic‐carbene‐catalysed 1,3‐dipolar cycloaddition of nitrile oxides and alkynes;5f and dipolar cycloaddition of acetylenic boronates4g,14 and silaacetylenes5j with nitrile oxides.…”