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Acylative Dimerization of Tetrahydrofuran Catalyzed by Rare‐Earth Triflates

“…When 1a is heated to 1408C in the presence of Yb(OTf) 3 (4 mol%), however, we do see the formation of THF and monomeric 2a, consistent with our observations of the distillation of the crude reaction mixtures and with the observations by Drysdale in the depolymerization of polytetrahydrofuran. [23] When aliquots are removed during the addition of THF to acetic anhydride using Yb(OTf) 3 (4 mol%), the ratio of 1a : 2a : higher oligomers does not change substantially. These control experiments rule out an equilibrium process favoring 1a, as has been proposed for the related reaction of THF with phosphorous oxychloride, [7] although there is significant equilibration of the products in the presence of the rare-earth catalysts at the temperatures necessary for distillation.…”

“…[22] The rare-earth metal triflates also are effective catalysts for the ring-opening reactions of highly strained epoxides and oxetanes giving monomeric products, [15] but the only reports in the literature concerning the cleavage reactions of tetrahydrofurans has been in their role as catalysts leading to polymeric materials. [23,24] Since these studies indicated the facile cleavage of cyclic ethers using rare-earth triflates, we decided to examine the acylative cleavage reactions of tetrahydrofuran catalyzed by ytterbium, scandium, or lanthanum triflate under conditions favoring low molecular weight products.…”