Alkyl- and Arylation of Oxacyclic Ethers with Triethylsilyl Triflate—2,4,6-Collidine—Gilman Reagent Combination: Remarkable Discrimination of Two Ether Oxygens

The alkylation reaction of oxacyclic ethers such as THP-ethers, THF-ethers, etc., has been developed.The treatment of oxacyclic ether with TESOTf and 2,4,6-collidine gives the collidinium salt intermediate obtained by the reaction of the cyclic oxygen atom.The addition of Gilman reagent to the mixture gives the alkylated product.The reaction proceeds with high chemoselectivity though there are two different oxygen atoms in the oxacyclic ethers.C-C bond formation is a fundamental reaction in organic synthesis.Recently, we succeeded in developing new C-C bond formation reactions of acetals with Gilman reagents via the collidinium intermediates i obtained from acetals (Scheme 1, eq. 1). 1 We then proposed to apply this reaction to oxacyclic ethers, because they also have acetal structures.However, two oxygen atoms in the oxacyclic ethers are different from each other, whereas the two oxygen atoms in the acetal function of eq. 1 are equivalent.When the reaction proceeds via the intermediate ii obtained by the reaction of the cyclic oxygen atom, a single product 4 would be obtained (Scheme 1, eq. 2a).