A chiral bicyclo[2.2.2]octa-2,5-diene ligand substituted with the ferrocenyl group and its use for rhodium-catalyzed asymmetric 1,4-addition reactions

Abstract

A chiral diene, (R,R)-Fc,Ph-bod, which bears the ferrocenyl (Fc) group and the phenyl (Ph) group on the bicyclo[2.2.2]octa-2,5-diene skeleton, has been synthesized, and its rhodium complex was examined as a catalyst for the asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated ketones. Its enantioselectivity was generally higher than that observed with (R,R)-Ph-bod, which is C 2 symmetric with two phenyl groups.Scheme 1 Synthesis of chiral bicyclo[2.2.2]octa-2,5-diene ligands by Abele. † Electronic supplementary information (ESI) available: Details of HPLC analysis of the addition products with chiral stationary phase columns. See

Chiral Diene Ligands in Asymmetric Catalysis

“…The alkylated and phenylated variations of the chiral bicyclo[2.2.1]­heptadiene scaffold ( L2–4 ) ,,,,, have shown excellent enantioselectivities in the rhodium-catalyzed asymmetric addition of PhB­(OH) 2 to enones. Other rigid chiral dienes, including bicyclo[2.2.2]­octadiene variations ( L6–15 ), ,,,,,,,,,,− , bicyclo[3.3.0]­octadiene variations ( L20–23 ), − ,,− , bicyclo[3.3.1]­nonadiene variations ( L16 , L18 , and L19 ), ,,, and bicyclo[3.3.2]­decadiene variations ( L17 ), were all reported to give excellent enantiomeric excesses. It is worth noting that the high catalytic activity of L8a is demonstrated by its strong performance in the 1,4-addition of PhB­(OH) 2 to 2-cyclohexenone and 2-cyclopentenone, which proceeds well with a low catalyst loading (0.01 mol % Rh) without any loss of catalytic activity or enantioselectivity (entry 6).…”

Enantioselective Synthesis of Spiro‐oxiranes: An Asymmetric Addition/Aldol/Spirocyclization Domino Cascade

“…Other chiral diene ligands developed by Carreira [20] were screened but gave lower yields and enantioselectivity (entry 6-8). Ultimately, by decreasing the reaction concentration and switching the chiral ligand to (S,S)-Fc,Ph-bod L2, [21] we arrived at the optimized conditions giving 78 % yield and 94 % ee (entry 9). In all cases, only a single diastereomer was observed.…”