34881-29-3Relevant articles and documents
Enantioselective addition of dimethylzinc to aldehydes catalyzed by a chiral perhydro-1,3-benzoxazine-based amino alcohol as ligand
Infante, Rebeca,Nieto, Javier,Andrs, Celia
, p. 1343 - 1348 (2012)
Dimethylzinc undergoes efficient enantioselective addition to a wide variety of aromatic and aliphatic aldehydes in the presence of a catalytic amount of a chiral perhydro-1,3-benzoxazine-based amino alcohol. Methyl carbinols are obtained in good yields and in enantiomeric excesses of 99% or more in the absence of any metal other than zinc. Georg Thieme Verlag Stuttgart · New York.
Broad Scope Synthesis of Ester Precursors of Nonfunctionalized Chiral Alcohols Based on the Asymmetric Hydrogenation of α,β-Dialkyl-, α,β-Diaryl-, and α-Alkyl-β-aryl-vinyl Esters
León, Félix,González-Liste, Pedro J.,García-Garrido, Sergio E.,Arribas, Inmaculada,Rubio, Miguel,Cadierno, Victorio,Pizzano, Antonio
, p. 5852 - 5867 (2017/06/07)
The catalytic asymmetric hydrogenation of trisubstituted enol esters using Rh catalysts bearing chiral phosphine-phosphite ligands (P-OP) has been studied. Substrates covered comprise α,β-dialkyl, α-alkyl-β-aryl, and α,β-diarylvinyl esters, the corresponding hydrogenation products being suitable precursors to prepare synthetically relevant chiral nonfunctionalized alcohols. A comparison of reactivity indicates that it decreases in the order: α,β-dialkyl > α-alkyl-β-aryl > α,β-diaryl. Based on the highly modular structure of P-OP ligands employed, catalyst screening identified highly enantioselective catalysts for α,β-dialkyl (95-99% ee) and nearly all of α-alkyl-β-aryl substrates (92-98% ee), with the exception of α-cyclohexyl-β-phenylvinyl acetate which exhibited a low enantioselectivity (47% ee). Finally, α,β-diarylvinyl substrates showed somewhat lower enantioselectivities (79-92% ee). In addition, some of the catalysts provided a high enantioselectivity in the hydrogenation of E/Z mixtures (ca. Z/E = 75:25) of α,β-dialkylvinyl substrates, while a dramatic decrease on enantioselectivity was observed in the case of α-methyl-β-anisylvinyl acetate (Z/E = 58:42). Complementary deuteration reactions are in accord with a highly enantioselective hydrogenation for both olefin isomers in the case of α,β-dialkylvinyl esters. In contrast, deuteration shows a complex behavior for α-methyl-β-anisylvinyl acetate derived from the participation of the E isomer in the reaction.
Majority-Rules-Type Helical Poly(quinoxaline-2,3-diyl)s as Highly Efficient Chirality-Amplification Systems for Asymmetric Catalysis
Ke, Yuan-Zhen,Nagata, Yuuya,Yamada, Tetsuya,Suginome, Michinori
, p. 9333 - 9337 (2015/08/06)
A highly efficient majority-rules effect of poly(quinoxaline-2,3-diyl)s (PQXs) bearing 2-butoxymethyl chiral side chains at the 6- and 7-positions was established and attributed to large ΔGh values (0.22-0.41 kJmol-1), which are defined as the energy difference between P- and M-helical conformations per chiral unit. A PQX copolymer prepared from a monomer derived from (R)-2-octanol (23% ee) and a monomer bearing a PPh2 group adopted a single-handed helical structure (>99%) and could be used as a highly enantioselective chiral ligand in palladium-catalyzed asymmetric reactions (products formed with up to 94% ee), in which the enantioselectivity could be switched by solvent-dependent inversion of the helical PQX backbone. Bowing to the majority: Poly(quinoxaline-2,3-diyl) containing PPh2 groups and chiral side chains derived from (R)-2-octanol with 23% ee exhibited a single-handed-helical conformation and served as a highly enantioselective chiral ligand in palladium-catalyzed reactions (see scheme; se=screw-sense excess). The chirality of the polymer could be switched by a solvent effect to enable the synthesis of the enantiomeric products.
Regio- and stereochemistry of Na-mediated reductive cleavage of alkyl aryl ethers
Azzena, Ugo,Carraro, Massimo,Meloni, Claudia,Murgia, Irene,Pisano, Luisa,Pittalis, Mario,Luisi, Renzo,Musio, Biagia,Degennaro, Leonardo
, p. 1550 - 1554 (2015/01/09)
We have investigated the regio-and stereochemistry of the reductive dealkoxylation of alkyl aryl ethers. Chiral non-racemic secondary alcohols were converted into the corresponding m-terphenyl or 2-biphenyl ethers either via inversion of configuration under Mitsunobu reaction conditions or with retention of configuration under SNAr conditions. The successive cleavage of the aromatic C-O bond occurred in the presence of a stoichiometric amount of Na metal in dry tetrahydrofuran at rt with retention of configuration, thus highlighting that the overall inversion or retention of configuration for the whole two-step procedure is dictated by the stereochemistry of the first synthetic step.
