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

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

The Journal of organic chemistry (2010-02-06)
Benjamin Bechem, Ryan L Patman, A Stephen K Hashmi, Michael J Krische
ABSTRACT

5-Substituted-2-furan methanols 1a-c are subject to enantioselective carbonyl allylation, crotylation and tert-prenylation upon exposure to allyl acetate, alpha-methyl allyl acetate, or 1,1-dimethylallene in the presence of an ortho-cyclometalated iridium catalyst modified by (R)-Cl,MeO-BIPHEP, (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 gamma-hydroxy-beta-pyrones 6a-c, respectively, with negligible erosion of enantiomeric excess.

MATERIALS
Product Number
Brand
Product Description

Supelco
Methyl acetate, analytical standard
Sigma-Aldrich
Methyl acetate, anhydrous, 99.5%
Sigma-Aldrich
Methyl acetate, ≥98%, FG
Sigma-Aldrich
Methyl acetate, natural, 98%, FG
Sigma-Aldrich
Methyl acetate, suitable for HPLC, ≥99.8%
Sigma-Aldrich
Methyl acetate, ReagentPlus®, 99%