The Role Ionic Liquid [BMIM][PF6] in One-Pot Synthesis of Tetrahydropyran Rings through Tandem Barbier–Prins Reaction

Abstract

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][PF6] through a Barbier–Prins reaction between allyl bromide and aldehydes. The use of [BMIM][PF6] gave Prins products from several aldehydes in good yields and reaction times. We also found that the anion, PF6-, accelerates the Barbier reaction when used alone, and the excess SnBr2 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.

An overview of recent advances in the catalytic synthesis of substituted pyrans

“…Batista et al [ 60 ] synthesized an ionic liquid [BMIM][PF 6 ] and examined their catalytic efficiency for the synthesis of pyran analogs using SnCl 2 .2H 2 O by Barbier–Prins reaction between allyl bromide and aldehydes. Prolonged reaction time (8 h) and moderate yields are the drawbacks of the designed pathway (Scheme 16).…”

“…Among the synthesized compounds, compounds bearing 2-furyl, 3-thiophenyl, 4-NO 2 , 4-hydroxy-3-methoxy groups were found to have remarkable IC 50 values. The aldehydes having electron withdrawing groups (EWG) gave high yields in less reaction time in comparison with aldehydes having electron donating substituents (EDG) (Scheme 15) Batista et al [60] synthesized an ionic liquid [BMIM] [PF 6 ] and examined their catalytic efficiency for the synthesis of pyran analogs using SnCl 2 .2H 2 O by Barbier-Prins reaction between allyl bromide and aldehydes. Prolonged reaction time (8 h) and moderate yields are the drawbacks of the designed pathway (Scheme 16).…”

Green synthesis, crystal structure, and antifungal activities of (E)-4-arylidene-5-oxotetrahydrofuran

“…On the other hand, assisted by microwave radiation, the rate of organic reaction is also greatly improved, and simple operation, high yield, simple post-treatment characteristics (Santagada et al, 2009;Sharma et al, 2012). Meanwhile, study has shown that ionic liquid [BMIM][PF 6 ] has a good role in the one-pot synthesis of tetrahydropyran ring in series Barbier-Prins reaction (Batista et al, 2019). Therefore, we tried to synthesize RPDFB RPDFC, RPDFI, RPDFJ in ionic liquid [BMIM][PF 6 ] and microwave-assisted as the continuation of previous research.…”