Study on the electronic effects on stereoconservativity of Suzuki coupling in chiral groove of binaphthyl

Synthesis, Resolution, and Absolute Configuration of Chiral 4,4′-Bipyridines

“…The use of bipyridine 3 as an enantiomerically pure precursor was then considered by studying the transfer of the stereochemical information after cross-coupling reactions. Such study on binaphthyl derivatives have shown stereoconservation or racemization depending on the organometallic counterpart (Mg, Zn, Sn, B, Al) and the reaction conditions. − In our case, complete stereoconservativity was observed after Suzuki and Sonogashira couplings with bipyridine ( M ) -3 demontrasting that bipyridine 3 is configurationally stable under palladium catalysis (Scheme ). This result indicates that both enantiomers of 3 can be used for the direct preparation of enantiomerically pure 4,4′-bipyridines.…”

Suzuki Cross‐Coupling at the Chiral Groove of 1,1′‐Binaphthyl: Stereoconservation versus Deracemization Pathway

“…Whereas Suzuki coupling at positions other than the 2‐ and 2′‐positions of 1,1′‐binaphthyl derivatives proceeds smoothly without impairment of the enantiomeric purity of the product,7 at the 2‐ and 2′‐positions, the reaction gives moderate yields of a coupling product that is almost completely racemized under standard conditions 8. Racemization during Suzuki cross‐coupling is most probably caused by the secondary oxidative addition of the common palladium(II) intermediate to the configurationally unstable palladium(IV) intermediate (Scheme ) 9,10…”

“…Indeed, we have shown that the stereochemical result of Suzuki diarylation at the 2‐ and 2′‐positions of the enantiopure binaphthyl precursor can be significantly affected by the leaving groups at the 2‐ and 2′‐positions; ditolylation by using triphenylphosphane as a ligand and barium hydroxide as a base yielded product 2 with 7 % ee from diiodide 1 ,8 95 % ee from dibromide,10 and >99 % ee from diboronic acid 8. Racemization of the binaphthyl moiety during diarylation of diiodide 1 can be suppressed by the use of less‐electron‐rich phosphane ligands,10 which decrease the ability of the palladium(II) intermediate to undergo secondary oxidative addition to the palladium(IV) intermediate. The best results were achieved in the case of trimethyl phosphite and triindol‐1‐ylphosphane (47 and 65 % ee of product 2 , respectively).…”

Use of the SPhos Ligand to Suppress Racemization in Arylpinacolboronate Ester Suzuki Couplings Involving α-Amino Acids. Synthesis of Biaryl Derivatives of 4-Hydroxyphenylglycine, Tyrosine, and Tryptophan

“…This issue has been addressed by several groups − and more systematic investigations have been carried out by both Hocek and ourselves . Hocek studied the Suzuki couplings of a phenylalaninylboronic acid with halopurine derivatives and circumvented racemization by switching from the Suzuki to a copper-mediated Stille coupling .…”