Enantioselective carbonyl allylation, crotylation, and tert- prenylation of furan methanols and furfurals via iridium-catalyzed transfer hydrogenation

Article abstract of DOI:10.1021/jo902697g

Chemical Equation Presentation 5-Substituted-2-furan methanols 1a-c are subject to enantioselective carbonyl allylation, crotylation and tertprenylation upon exposure to allyl acetate, a-methyl allyl acetate, or 1, 1-dimethylallene in the presence of an orthocyclometalated iridium catalyst modified by (R)-Cl,MeOBIPHEP, (R)-C3-TUNEPHOS, and (R)-C3-SEGPHOS, respectively. In the presence of 2-propanol, but under otherwise identical conditions, the corresponding substituted furfurals 2a-c are converted to identical products of allylation, crotylation, and tert-prenylation. Optically enriched products of carbonyl allylation, crotylation, and reverse prenylation 3b, 4b, and 5b were subjected to Achmatowicz rearrangement to furnish the corresponding γ-hydroxy-β-pyrones 6a-c, respectively, with negligible erosion of enantiomeric excess.