Titanium-Catalyzed Reductive Umpolung Reactions with a Metal-Free Terminal Reducing Agent
作者:Georg Frey、J. Niklas Hausmann、Jan Streuff
DOI:10.1002/chem.201500102
日期:2015.4.7
A newmethod for titanium-catalyzed reductive umpolung reactions is reported that overcomes the traditional requirement for a stoichiometric metallic reductant. With N,N'-disilylated tetramethyldihydropyrazine as a potent organic reducing agent, reductive carbonyl-nitrile, enone-acrylonitrile and pinacolcouplingreactions can be achieved in good yields and stereoselectivities. [Cp2TiI2] is a superior
The addition of arylstannanes to the carbon–heteroatom double bond in the presence of a catalytic amount of a cationic rhodium complex ([Rh(cod)(MeCN)2]BF4) was examined. The reactions of aldehydes, α-dicarbonyl compounds, and N-substituted aldimines with the arylstannanes gave corresponding alcohols, α-hydroxy carbonyl compounds, and amines, respectively. An arylrhodium complex generated by the transmetalation
nitriles is described, which gives direct access to alpha-hydroxylated and alpha-aminated ketones. This coupling reaction is cross-selective and a catalytic version of the classical acyloincondensation. A reaction mechanism that is supported by first DFT calculations is discussed.
Novel Routes to Enol Ethers, Unsymmetrical Ketones, .alpha.-Bromoalkyl Ketones, 1,4-Diketones, 2-Ethoxy-2-cyclopentenones, and .alpha.-Keto Enamines
作者:Alan R. Katritzky、Guifen Zhang、Jinlong Jiang
DOI:10.1021/jo00128a037
日期:1995.11
Highly regioselective S(N)2' reactions of adducts 6 (readily prepared by reactions of halides with the allyl anion 12 of 11) with Grignard reagents gave enol ethers 13, which were converted (in one-pot reactions from 11) into ketones 14 and alpha-bromoalkyl ketones 15 in good yields. The monoprotected 1,4-diketone derivative 16 (prepared by Michael addition of the allyl anion 12 with methyl vinyl ketone) was converted both into 1,4-diketones 18 and into protected gamma-hydroxyalkyl ketone 20 by selective Grignard reactions, which could be directed either to the carbonyl, or the protected propenoyl, or to both functionalities. The allyl anion 12 with alpha-substituted acetic esters gave alpha-acylated adducts 24, which underwent in situ unfavored endo-trig cyclization upon treatment with NaH and secondary amines, to give 2-ethoxy-2-cyclopentenones 27 and 28 and alpha-keto enamines 25 in good yield. The mechanism for the cyclization is discussed.
Mamlok; Wiemann, Bulletin de la Societe Chimique de France, 1954, p. 1424,1426