Published on Web 11/17/2007
Asymmetric Allylboration of Acyl Imines Catalyzed by Chiral Diols Sha Lou, Philip N. Moquist, and Scott E. Schaus* Contribution from the Department of Chemistry and Center for Chemical Methodology and Library DeVelopment, Life Science and Engineering Building, Boston UniVersity, 24 Cummington Street, Boston, Massachusetts 02215 Received July 28, 2007; E-mail:
[email protected] Abstract: Chiral BINOL-derived diols catalyze the enantioselective asymmetric allylboration of acyl imines. The reaction requires 15 mol % (S)-3,3′-Ph2-BINOL as the catalyst and allyldiisopropoxyborane as the nucleophile. The reaction products are obtained in good yields (75-94%) and high enantiomeric ratios (95:5-99.5:0.5) for aromatic and aliphatic imines. High diastereoselectivities (diastereomeric ratio > 98:2) and enantioselectivities (enantiomeric ratio > 98:2) are obtained in the reactions of acyl imines with crotyldiisopropoxyboranes. This asymmetric transformation is directly applied to the synthesis of Maraviroc, the selective CCR5 antagonist with potent activity against HIV-1 infection. Mechanistic investigations of the allylboration reaction including IR, NMR, and mass spectrometry studies indicate that acyclic boronates are activated by chiral diols via exchange of one of the boronate alkoxy groups with activation of the acyl imine via hydrogen bonding.
Introduction
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Allylboration of Acyl Imines Catalyzed by Chiral Diols
ARTICLES
Table 1. Asymmetric Allylboration of Acyl Iminesa
entry
catalyst
mol %b
% yieldc
erd
1 2 3 4 5 6 7 8 9 10 11 12
7a 7b 7c 7d 7e 7f 7g 7h 7h 7h 7i
15 15 15 15 15 15 10 15 10 5 15
