Efficient method for the preparation of pinacols derived from aromatic and aliphatic ketones by using low-valent titanium reagents in dichloromethane-pivalonitrile
aldehydes and ketones, including unsymmetrical aliphatic ketones, proceeded smoothly to give the corresponding pinacols in good to high yields under mild conditions by using combination of titanium(II) chloride and zinc or titanium(IV) chloride and zinc in dichloromethane-pivalonitrile. Meso-selective formation of the coupling products was observed in the cases of some aliphatic ketones. The diastereoselectivities
Iron-catalyzed Pinacol Coupling of Aryl Ketones with a Phenyltitanium Reagent: A New Type of Catalytic Reaction
作者:Tamio Hayashi、Keigo Sasaki
DOI:10.1246/cl.2011.492
日期:2011.5.5
A reaction of aryl ketones with phenyltitanium triisopropoxide ([PhTi(Oi-Pr)3]) in the presence of [Fe(acac)3] as a catalyst (1 mol %) gave the corresponding pinacols in high yields. The catalytic cycle of this process involves an iron-catalyzed disproportionation of [PhTi(Oi-Pr)3] into biphenyl and a low-valent titanium species.
(I) is a mixture of the two possible conformers. For the gauche conformer of I an OH… π-electrons H-bond is proposed in addition to the OH.. O H-bond. The magneticnonequivalence of the isopropyl methyls is solvent independent for II and proportional to the logarithm of the dielectric constant of the solvent for I. An interpretation of these findings in terms of conformational preferences is proposed
分配给2,5-二甲基-3,4-二苯基-3,4-己二醇的非对映异构体的内消旋和dl构型已经基于IR和PMR光谱。dl异构体(II)解释为主要由具有OH基gauche和异丙基anti的构象异构体表示,而内消旋异构体(I)是两种可能的构象异构体的混合物。对于薄纱除了OH .. O H键以外,还提出了OH…π电子H键的构象异构体。异丙基甲基的磁性非等价性与溶剂无关,与溶剂II的介电常数对数成正比。dl异构体II的异丙基甲基的Δτ值是报道的最大值(在各种溶剂中为0·84-0.90 ppm)。
Efficient Method for Pinacol Coupling of Aromatic and Aliphatic Ketones by Using Titanium(II) Chloride and Zinc in the Presence of Pivalonitrile
coupling reaction of aromatic and aliphatic ketones including acyclic aliphatic ketones proceeded smoothly to give the corresponding pinacols in good to high yields below room temperature by the combined use of titanium(II) chloride and zinc in the presence of pivalonitrile. Meso-selective formation of the coupling products was observed in the cases with some acyclic aliphatic ketones.