Synthesis of α-hydroxy carboxylic derivatives by 1,2-addition
A combination of weak Lewis acid (LiCl) and weak Brønsted acid (hexafluoroisopropanol, HFIP) promotes efficiently the Friedel-Crafts reaction of electron-rich aromatic compounds with ethyl glyoxylate.
M. Willot, J. Chen, J. Zhu, Synlett, 2009, 577-580.
The asymmetric Friedel-Crafts reaction of N,N-dialkylanilines with ethyl glyoxylate has been achieved by the catalysis of titanium complexes of BINOL derivatives to give the corresponding mandelic acid ethyl esters in high yields (85-99%) and good to excellent enantioselectivity (80-96.6% ee).
Y. Yuan, X. Wang, X. Li, K. Ding, J. Org. Chem., 2004, 69, 146-149.
Chiral allenes appended with basic functionality can serve as ligands for transition metals. An allene-containing bisphosphine coordinated to Rh(I) promotes the asymmetric addition of arylboronic acids to α-keto esters with high enantioselectivity. Solution and solid-state structural analysis reveals that one olefin of the allene can coordinate to transition metals, generating bi- and tridentate ligands.
F. Cai, X. Pu, X. Qi, V. Lynch, A. Radha, J. M. Ready, J. Am. Chem. Soc., 2011, 133, 18066-18069.
The tandem ylide formation/[2,3]-sigmatropic rearrangement between donor/acceptor rhodium carbenoids and chiral allyl alcohols generates two vicinal stereogenic centers in a convergent C-C bond forming process. Any of the four possible stereoisomers can be selectively synthesized by appropriate combination of the chiral catalyst Rh2(DOSP)4 and the chiral alcohol.
Z. Li, B. T. Parr, H. M. L. Davies, J. Am. Chem. Soc., 2012, 134, 10942-10946.