FeCl3-mediated efficient method for the synthesis of tetrahydropyran derivatives via crosscyclization of epoxides and homoallylic alcohols

Background: An efficient methodology for the synthesis of tetrahydropyran derivatives has been developed under mild reaction conditions. The reactions were carried out using epoxides and homoallylic alcohols as reactants and ferric chloride as catalyst. All the reactions were done at room temperature in methylene dichloride. Results: In all cases, the reactions proceeded efficiently at ambient temperature under mild conditions showing the generality of the reaction. The reaction also proceeded well with the cyclic epoxide 1,2-dihydronaphthalene oxide to give the corresponding spirotetrahydropyrans in good yield. The proton on the carbon bearing the halide group (4-H) (δ 3.80, J = 4.46 and 11.80 Hz) shows NOE with the proton on the carbons bearing the benzyl group (2-H) (δ 3.46, J = 11.80 Hz) and the proton on the carbon bearing the methyl group (6-H) (δ 3.40, J = 11.80 Hz). This confirms that the protons 2-H, 4-H, and 6-H are on the same side and occupy the axial position of a chair conformation. Conclusion: The attractive features of this process are mild reaction conditions, which are environmentally friendly, inexpensive reagents, with short reaction times, and cleaner reactions with improved yields, which make it a useful process for the synthesis of tetrahydropyran derivatives.