Enantioselective carbonyl allylation, crotylation, and tert-prenylation of furan methanols and furfurals via iridium-catalyzed transfer hydrogenation.
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.
Bechem
Benjamin
B
Organisch-Chemisches Institut Ruprecht-Karls-Universität Heidelberg, D-69120 Heidelberg, Germany.
Patman
Ryan L
RL
Hashmi
A Stephen K
AS
Krische
Michael J
MJ
D000085:Acetates / Q000737:chemistry*; D000498:Allyl Compounds / Q000737:chemistry*; D002384:Catalysis; D005662:Furaldehyde / Q000737:chemistry*; D005663:Furans / Q000737:chemistry*; D006865:Hydrogenation; D007495:Iridium / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry*; D015394:Molecular Structure; D011753:Pyrones / Q000737:chemistry*; D013237:Stereoisomerism
D000085:Acetates; D000498:Allyl Compounds; D005663:Furans; D011753:Pyrones; D007495:Iridium; D005662:Furaldehyde; C498551:allyl acetate; C039281:furan; C046923:methyl acetate; D000432:Methanol