Hai-Feng Duan

Enantioselective Rhodium‐Catalyzed Addition of Arylboronic Acids to α‐Ketoesters

The transition-metal-catalyzed asymmetric addition of organometallic reagents to carbonyl compounds to produce enantiomer-enriched secondary or tertiary alcohols is a powerful tool for the construction of carbon–carbon bonds. Many organometallic reagents have been successfully used in this addition reaction. However, a drawback for most organometallic reagents is their sensitivity to moisture and air, both of which impede the practical applications of these asymmetric carbon–carbon bond-forming reactions. As an exception, arylboronic acids are very stable to air and moisture. The catalytic enantioselective addition of arylboronic acids to carbonyl compounds has became a current focus for research, and a number of efficient chiral catalysts have been developed for the catalytic asymmetric addition of arylboronic acids to aldehydes and aldimines. However, the catalytic asymmetric addition of arylboronic acids to ketones, which are less active relative to aldehydes and aldimines, is more difficult, and only limited progress has been achieved. In 2006, Hayashi et al. reported the asymmetric addition of arylboronic acids to isatins, cyclic aketoamides, catalyzed by a rhodium/MeO-Mop (MeO-Mop = 2-methoxy-2’-diphenylphosphino-1,1’-binaphthyl) complex in high enantioselectivities (72–91 % ee). By using a chiral phosphoramidite ligand derived from H8-binol (binol = 2,2’dihydroxy-1,1’-binaphthyl), de Vries, Minnard, Feringa and et al. obtained 55 % ee in the same reaction. The chiral phosphoramidite ligand was also used in the asymmetric addition of arylboronic acids to trifluoromethyl ketones with good enantioselectivities (50–83 % ee). The intramolecular asymmetric addition of arylboronic acids to ketones catalyzed by a cationic palladium complex of binap (binap = 2,2’bis(diphenylphosphanyl)-1,1’-binaphthyl) to give cyclic tertiary alcohols in high enantioselectivities (53–96% ee) was reported by Lu et al. To the best of our knowledge, the catalytic enantioselective addition of arylboronic acids to aketoesters to provide tertiary a-hydroxyesters has not yet been reported. In the search for highly efficient methods to construct chiral 2-hydroxydiarylacetates, desirable chiral intermediates for the synthesis of antagonists of muscarinic receptors, we became interested in the enantioselective addition of arylboronic acids to the a-aryland a-alkenyl-a-ketoesters. The Rh/ShiP (ShiP = aryl(1,1’-spirobiindane-7,7’-diyl)phosphite) catalysts (1) recently developed by us were found to be

Asymmetric Friedel-Crafts Addition of Indoles to N-Sulfonyl Aldimines

[reaction: see text] The enantioselective copper(II)-catalyzed Friedel-Crafts addition of indoles to N-sulfonyl aldimines was developed using chiral bisoxazoline as ligands, and high enantioselectivities (up to 96% ee) were achieved.

Rh-Catalyzed Arylation of N-Tosylarylimines with Arylboronic Acids

The asymmetric arylation of N-tosylarylimines with arylboronic acids was realized by using rhodium/(S)-ShiP as catalyst. The reaction proceeded in aqueous toluene to give diarylmethylamines in good yields with up to 96% ee. [reaction: see text]