<b>PQXdpap</b>: Helical Poly(quinoxaline-2,3-diyl)s Bearing 4-(Dipropylamino)pyridin-3-yl Pendants as Chirality-Switchable Nucleophilic Catalysts for the Kinetic Resolution of Secondary Alcohols
Helically chiral poly(quinoxaline-2,3-diyl)s bearing 4-(dipropylamino)pyridin-3-yl pendants at the 5-position of the quinoxaline ring (PQXdpap) exhibited high catalytic activities and moderate to high selectivities (up to s = 87) in the acylative kinetic resolution of secondary alcohols. The solvent-dependent helical chirality switching of PQXdpap between pure toluene and a 1:1 mixture of toluene and
of aldehyde by the catalysis of a chiraltitaniumcomplex derived from DTBP-H8-BINOL. The reaction is performed with good stoichiometry [1.5 equiv each of Grignard reagents and ClTi(OiPr)3] at a low catalyst loading (2 mol %), affording a variety of chiral secondary alcohols in high enantioselectivity and yields and, hence, realizing an asymmetric version of the Grignard reaction in an indirect manner
由格氏试剂和ClTi(O i Pr)3原位生成的烷基钛试剂可通过催化衍生自DTBP-H 8 -BINOL的手性钛配合物用于醛的对映选择性烷基化反应,而无需进一步操作。该反应以良好的化学计量[1.5当量的格氏试剂和ClTi(O i Pr)3 ]在低催化剂负载量(2mol%)下进行,从而以高对映选择性和收率提供了多种手性仲醇,因此,间接实现格氏反应的不对称形式。
Enantioselective Alkylation of Aldehydes Using Functionalized Alkylboron Reagents Catalyzed by a Chiral Titanium Complex
作者:Ravindra Kumar、Hiroki Kawasaki、Toshiro Harada
DOI:10.1021/ol4019248
日期:2013.8.16
A practical method is developed for the synthesis of enantioenriched functionalized secondary alcohols through catalytic enantioselective alkylation of aldehydes. Functionalized alkylboron reagents, [FG–(CH2)n]3B (FG = Br, TIPSO, PhtN, CO2iPr, and CN) prepared from terminal olefin precursors by hydroboration, undergo enantioselective addition to aldehydes in the presence of a catalytic amount (5 mol