Asymmetric cyclopropanation of electron-rich alkenes by the racemic diene rhodium catalyst: the chiral poisoning approach.

Asymmetric cyclopropanation of alkenes by aryldiazoacetates was achieved using the readily-available racemic (diene)rhodium complex in combination with the chiral oxazoline-phenol ligand, which acts as the chiral poison and selectively inhibits one of the enantiomers of the catalyst. This approach eliminates a common problematic step of the synthesis of chiral catalysts.

Planar Chiral Rhodium Complexes of 1,4-Benzoquinones.

Diene rhodium complexes are important catalysts in modern organic synthesis. Herein, we report a new approach to such complexes with the uncommon planar chirality. The synthesis is achieved by face-selective coordination of the prochiral 2,5-disubstituted-1,4-benzoquinones (R2 -Q) with rhodium precursors containing the chiral auxiliary ligand S-salicyl-oxazoline (S-Salox). Such coordination leads to the formation of (R,R-R2 -Q)Rh(S-Salox) complexes in high yields and with exceptional diastereoselectivity (d. r.>20 : 1). Subsequent replacement of the auxiliary ligand provides various benzoquinone rhodium complexes with retention of the planar chirality. Combined theoretical and experimental studies show that due to their electron-withdrawing nature benzoquinones bind metals stronger than the related 1,4-cyclohexadiene, but weaker than other common diene ligands, such as cyclooctadiene.

Synthesis of Rhodium Complexes with Chiral Diene Ligands via Diastereoselective Coordination and Their Application in the Asymmetric Insertion of Diazo Compounds into E-H Bonds.

A new method for the synthesis of chiral diene rhodium catalysts is introduced. The readily available racemic tetrafluorobenzobarrelene complexes [(R2 -TFB)RhCl]2 were separated into two enantiomers via selective coordination of one of them with the auxiliary S-salicyl-oxazoline ligand. One of the resulting chiral complexes with an exceptionally bulky diene ligand [(R,R-iPr2 -TFB)RhCl]2 was an efficient catalyst for the asymmetric insertion of diazoesters into B-H and Si-H bonds giving the functionalized organoboranes and silanes with high yields (79-97 %) and enantiomeric purity (87-98 % ee). The stereoselectivity of separation via auxiliary ligand and that of the catalytic reaction was predicted by DFT calculations.

Rhodium(III) Complex with a Bulky Cyclopentadienyl Ligand as a Catalyst for Regioselective Synthesis of Dihydroisoquinolones through C-H Activation of Arylhydroxamic Acids.

Catalytic reaction of arylhydroxamic acids with alkenes represents a convenient method for preparation of biologically active dihydroisoquinolones. Here, the rhodium(III) complex [(C5 H2 tBu2 CH2 tBu)RhCl2 ]2 , which allows one to carry out such reactions with high regioselectivity to obtain 4-substituted dihydroisoquinolones in 72-97 % yields, is described. The regioselectivity is provided by the bulky cyclopentadienyl ligand of the catalyst, which is formed through a [2+2+1] cyclotrimerization of tert-butylacetylene. The catalytic reaction tolerates various distant functional groups in alkenes, but is inhibited by bulky (e.g., tBu) or strongly coordinating (e.g., imidazolyl) substituents. Some of the prepared dihydroisoquinolones effectively inhibit growth of phytopathogenic fungi.

A Planar-Chiral Rhodium(III) Catalyst with a Sterically Demanding Cyclopentadienyl Ligand and Its Application in the Enantioselective Synthesis of Dihydroisoquinolones.

The rapid development of enantioselective C-H activation reactions has created a demand for new types of catalysts. Herein, we report the synthesis of a novel planar-chiral rhodium catalyst [(C5 H2t Bu2 CH2t Bu)RhI2 ]2 in two steps from commercially available [(cod)RhCl]2 and tert-butylacetylene. Pure enantiomers of the catalyst were obtained through separation of its diastereomeric adducts with natural (S)-proline. The catalyst promoted enantioselective reactions of aryl hydroxamic acids with strained alkenes to give dihydroisoquinolones in high yields (up to 97 %) and with good stereoselectivity (up to 95 % ee).