Pt-Catalyzed Cyclization of Propargylic Oxiranes to Substituted Furans

Significance

Reported here is a Pt-catalyzed synthetic methodology for the conversion of propargylic oxiranes into 2-substituted furans in aqueous media. Whereas the catalytic reaction using AuCl₃ in acetonitrile was previously found to be sluggish (21% yield in 36 h, see A. S. K. Hashmi, P. Sinha Adv. Synth. Cat. 2004, 346, 432) and the corresponding Pt-catalyzed reaction in dioxane in the absence of water required 3 h (90% yield) for completion, dioxane-H₂O (2:1) at 100 ˚C with 10 mol% Pt catalyst was found to be optimal. Using deuterated water gave the product with 97% incorporation of deuterium at C3, a result consistent with the depicted mechanism. Trapping of the furanyl-platinum species with iodine gave the 3-iodofuran, which clearly has potential for fur-ther functionalization by cross-coupling chemistry as shown in the scheme.