Enantioselective carbonyl reverse prenylation from the alcohol or aldehyde oxidation level employing 1,1-dimethylallene as the prenyl donor.
Enantioselective transfer hydrogenation of 1,1-dimethylallene 1a in the presence of aromatic, alpha,beta-unsaturated, or aliphatic aldehydes 2a-i mediated by 2-propanol and employing a cyclometalated iridium C,O-benzoate derived from allyl acetate, m-nitrobenzoic acid, and (S)-SEGPHOS delivers reverse-prenylation products 4a-i in good to excellent isolated yields (65-96%) and enantioselectivities (87-93% ee). In the absence of 2-propanol, enantioselective carbonyl reverse prenylation is achieved directly from the alcohol oxidation level to furnish an equivalent set of adducts 4a-i in good to excellent isolated yields (68-94%) and enantioselectivities (86-91% ee). Competition and isotopic labeling experiments suggest rapid alcohol-aldehyde redox equilibration in advance of carbonyl addition along with capture of the kinetically formed pi-allyl complex at a higher rate than reversible beta-hydride elimination-hydrometalation. This protocol represents an alternative to the use of allylmetal reagents in enantioselective carbonyl reverse prenylation and represents the first use of allenes in enantioselective C-C bond-forming transfer hydrogenation.
Han
Soo Bong
SB
University of Texas at Austin, Department of Chemistry and Biochemistry, Austin, Texas 78712, USA.
Kim
In Su
IS
Han
Hoon
H
Krische
Michael J
MJ
D000438:Alcohols / Q000138:chemical synthesis* / Q000737:chemistry; D000447:Aldehydes / Q000737:chemistry*; D000466:Alkadienes / Q000737:chemistry*; D000475:Alkenes / Q000138:chemical synthesis* / Q000737:chemistry; D001565:Benzoates / Q000737:chemistry; D002384:Catalysis; D007495:Iridium / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry; D010084:Oxidation-Reduction; D010720:Phosphines / Q000737:chemistry; D054876:Prenylation; D013237:Stereoisomerism
D000438:Alcohols; D000447:Aldehydes; D000466:Alkadienes; D000475:Alkenes; D001565:Benzoates; D009942:Organometallic Compounds; D010720:Phosphines; D007495:Iridium; C025947:propadiene