The Role Ionic Liquid [BMIM][PF(6)] in One-Pot Synthesis of Tetrahydropyran Rings through Tandem Barbier–Prins Reaction

Tetrahydropyran (THP) rings are common in several natural products, therefore, various strategies are being developed to synthesize these rings. The present work described the study of a one-pot synthesis of 2,4,6-trisubstituted tetrahydropyran compounds promoted by the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF(6)] through a Barbier–Prins reaction between allyl bromide and aldehydes. The use of [BMIM][PF(6)] gave Prins products from several aldehydes in good yields and reaction times. We also found that the anion, PF(6)-, accelerates the Barbier reaction when used alone, and the excess SnBr(2) from the reaction conditions of the Barbier reaction leads to the formation of the THP rings, thus acting as a catalyst for Prins cyclization. Additionally, we demonstrate that ionic liquid can be recovered and reused five times in the preparation of 4-bromo-tetrahydro-2,6-diphenyl-2H-pyran without significant yield loss.