Abstract
A new bidentate phosphoramidite (N-Me-BIPAM) based on Shibasaki’s N-linked BINOL was synthesized. This ligand appears to be highly effective for rhodium-catalyzed asymmetric conjugated addition of arylboronic acids to α,β-unsaturated enones. The reaction of ortho-substituted arylboronic acid with acyclic and cyclic enones provides the corresponding products in good yields and enantioselectivities.
Highlights
Metal-catalyzed conjugated addition reactions of carbon nucleophiles to α,β-unsaturated compounds are the most widely used reactions for asymmetric carbon-carbon bond formation [1,2,3]
Much interest has recently been shown in rhodium-catalyzed conjugate addition of arylboronic acids to α,β-unsaturated carbonyl compounds [1,2,3,4,5,6,7,8] using various ligands [9,10,11,12,13,14,15,16,17,18,19,20,21] such as biaryl bisphosphines [4,5,6,7,8], phosphoramidites [22,23,24,25,26,27,28], diphosphonite [29], amidomonophosphines [30,31], N-heterocyclic carbenes [32,33], P-chiral phosphine [34], and dienes [35,36,37,38,39,40,41,42,43]
Molecules 2013, 18 was synthesized and that a rhodium/Me-BIPAM complex was a better catalyst than several monodentate phosphoramidites for conjugate addition of arylboronic acids to α,β-unsaturated cyclic and acyclic carbonyl compounds [53,54]
Summary
Metal-catalyzed conjugated addition reactions of carbon nucleophiles to α,β-unsaturated compounds are the most widely used reactions for asymmetric carbon-carbon bond formation [1,2,3]. Though conjugate addition of ortho-substituted arylboronic acids to α,β-unsaturated cyclic enones has been achieved in high enantioselectivities [9,10,11,12,13,14,15,16,17,18,19,20,21,44,45,46,47,48,49,50], there have been few reports on this reaction for acyclic enones [38,51,52]. We reported that the bidentate phosphoramidite N-Me-BIPAM, which was newly synthesized on the basis of N-linked-BINOL [55], was highly efficient for rhodium-catalyzed asymmetric arylation of N-sulfonyl aldimine with arylboronic acids [56]. N-Me-BIPAM was necessary to achieve high enantioselectivity for the reaction of ortho-substituted arylboronic acids to acyclic and cyclic enones
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