Asymmetric Friedel–Crafts reaction of furans with alkyl glyoxylates catalyzed by (salen)Co(II) complexes

Highly Enantioselective Synthesis of 2-Furanyl-hydroxyacetates from Furans via the Friedel−Crafts Reaction

“…It was of interest for us to find an efficient and readily accessible catalytic system for the reaction of furans with glyoxylates. Jørgensen’s and our studies in this field showed that bisoxazoline and salen metal complexes were not efficient enough in this case. We focused our attention on chiral BINOL-type ligands and found that their complexes with Ti(IV), generated from BINOL and Ti(OPr i ) 4 , were efficient catalysts for this reaction.…”

“…We focused our attention on the asymmetric F−C reactions of furans with active aldehydes, namely, glyoxylates, including diastereoselective and enantioselective approaches . The products of this reaction, 2-furanyl-hydroxyacetic acid esters ( I ) (Scheme ), are very interesting building blocks for the synthesis, and after reduction to diols II , these synthons can be transformed under oxidizing conditions to linear ( III ) as well as cyclic products, e.g., dihydropyranones ( IV ) or dihydropyridones ( V ).…”

“…Recently, we published a highly diastereoselective reaction of furans with chiral (1 R ,2 S ,5 R )-8-phenylmenthyl glyoxylate promoted by magnesium bromide . Our previous attempts with chiral catalysts, e.g., salen−cobalt complexes, led to the F−C products of moderate enantioselectivity (up to 76% ee) . The catalytic enantioselective version of this reaction with bisoxazoline−copper complexes was also investigated by Jørgensen and co-workers, although, in the case of reaction of 2-methylfuran (silvan) and ethyl glyoxylate, the enantioselectivity was low (45% ee), in contrast to high ee values in the case of anilines (usually >80% ee).…”

Hyperbaric reactions in organic synthesis. Progress from 2006 to 2021

“…The asymmetric catalytic variant of the Friedel-Crafts reaction of 2-alkylfurans 232 with alkyl glyoxalates 233 was studied by the same research team (Scheme 76), 134 and it was found that the reaction can be carried out at both atmospheric and high pressure (6-10 kbar) in the presence of (salen) cobalt catalysts. It is noteworthy that hyperbaric conditions not only increased the yield but also significantly influenced the asymmetric induction, with enantioselectivity increasing from 44 to Scheme 74 Hyperbaric enantioselective hydroxyalkylation of indoles.…”

Catalytic Enantioselective Reactions of Biomass-Derived Furans

“…As a result, chiral 2-alkylated products 55 were obtained in high yields (73-93) with low to moderate enantioselectivities (25-62% ee) (Figure 17) [33]. Another attempt with regard to the asymmetric Friedel-Crafts reaction of furans 36 with alkyl glyoxalates 57 utilizing Jacobsen's Co(II)-salen complexes 56 as a catalyst was accomplished by the Jurczak group in 2006 (Figure 18) [34]. Highpressure (ca.…”