Reactivity and enantioselectivity in the reactions of scalemic stereogenic alpha-(N-carbamoyl)alkylcuprates.
Stereogenic 2-(N-carbamoyl)pyrrolidinylcuprates prepared from scalemic (i.e., enantioenriched) N-Boc-2-lithiopyrrolidine and THF soluble CuCN.2LiCl react with vinyl iodides, vinyl triflates, beta-iodo-alpha,beta-enoates, propargyl mesylates, and allyl bromide to afford the substitution products with excellent enantioselectivity. Excellent enantiomeric ratios are obtained in the conjugate addition reactions with methyl vinyl ketone while low enantiomeric ratios can be achieved with acrylate esters using HMPA/TMSCl activation. Enantiomeric ratios vary with substrate substitution patterns and the observed enantioselectivities appear to be more a function of cuprate-electrophile reactivities than of the reaction type (e.g., substitution, conjugate addition). Low enantiomeric ratios are obtained with the alpha-(N-carbamoyl)benzylcuprates. The lithium-copper transmetalation and cuprate vinylation reactions proceed with retention of configuration.
Dieter
R Karl
RK
Howard L. Hunter Laboratory, Department of Chemistry, Clemson University, Clemson, South Carolina 29634-0973, USA. dieterr@clemson.edu
Oba
Gabriel
G
Chandupatla
Kishan R
KR
Topping
Chris M
CM
Lu
Kai
K
Watson
Rhett T
RT
D000478:Alkylation; D000498:Allyl Compounds / Q000737:chemistry; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003510:Cyclohexanes / Q000737:chemistry; D018020:Lithium Compounds / Q000737:chemistry; D008698:Mesylates / Q000737:chemistry; D008782:Methylurea Compounds / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D011759:Pyrrolidines / Q000737:chemistry; D013237:Stereoisomerism; D014753:Vinyl Compounds / Q000737:chemistry
D000498:Allyl Compounds; D003510:Cyclohexanes; D018020:Lithium Compounds; D008698:Mesylates; D008782:Methylurea Compounds; D009942:Organometallic Compounds; D011759:Pyrrolidines; D014753:Vinyl Compounds; D003300:Copper; C050431:allyl bromide; C006892:carbamol