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. 2010 May 21;75(10):3317-25.
doi: 10.1021/jo100312w.

Lanthanum tricyanide-catalyzed acyl silane-ketone benzoin additions and kinetic resolution of resultant alpha-silyloxyketones

James C Tarr  1 , Jeffrey S Johnson
Affiliations

Lanthanum tricyanide-catalyzed acyl silane-ketone benzoin additions and kinetic resolution of resultant alpha-silyloxyketones

James C Tarr et al. J Org Chem. .

Abstract

We report the full account of our efforts on the lanthanum tricyanide-catalyzed acyl silane-ketone benzoin reaction. The reaction exhibits a wide scope in both acyl silane (aryl, alkyl) and ketone (aryl-alkyl, alkyl-alkyl, aryl-aryl, alkenyl-alkyl, alkynyl-alkyl) coupling partners. The diastereoselectivity of the reaction has been examined in both cyclic and acyclic systems. Cyclohexanones give products arising from equatorial attack by the acyl silane. The diastereoselectivity of acyl silane addition to acyclic alpha-hydroxy ketones can be controlled by varying the protecting group to obtain either Felkin-Ahn or chelation control. The resultant alpha-silyloxyketone products can be resolved with selectivity factors from 10 to 15 by subjecting racemic ketone benzoin products to CBS reduction.

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Figures

Figure 1
Figure 1
Previous examples of intra- and intermolecular-ketone benzoin reactions
Figure 2
Figure 2
NOESY Analysis to Determine Equatorial Attack
Figure 3
Figure 3
NOESY Analysis to Confirm Felkin-Ahn and Chelation Controlled Addition
Figure 4
Figure 4
Proposed mechanistic pathway for acyl silane-ketone benzoin reaction (black) and possible side reactions (gray).
Figure 5
Figure 5
NHC-catalyzed retro-benzoin reaction of tertiary α-hydroxyketone
Scheme 1
Scheme 1
Addition of Acyl Silane to Diaryl Ketones
Scheme 2
Scheme 2
Optimized Conditions for Achieving Felkin-Ahn or Chelation Control
Scheme 3
Scheme 3
Kinetic Resolution of α-Silyloxy Ketones via CBS Reduction
Scheme 4
Scheme 4
Determination of Absolute Configuration of Enantioenriched Product
See this image and copyright information in PMC

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