Reactions of Aliphatic Ketones R2CO (R=Me, Et,iPr, andtBu) with the MCl4/Li(Hg) System (M=U or Ti): Mechanistic Analogies between the McMurry, Wittig, and Clemmensen Reactions
system (M = U, Ti) at 20 degrees C revealed significant differences. For R = Me, the reaction proceeded exclusively (M = U) or preferentially (M = Ti) via a metallopinacol intermediate resulting from dimerization of ketylradicals. Pinacol was liberated by hydrolysis, and tetramethylethylene was obtained after further reduction at 65 degrees C. For R=iPr, formation of iPr2C=CiPr2 as the only coupling
Activation of Low-Valent Titanium Reagents with Iodine: Facile Low-Temperature McMurry Reaction and <i>N</i>/<i>O</i>-Debenzylation/Deallylation
作者:Sanjay Talukdar、Sandip K. Nayak、Asoke Banerji
DOI:10.1021/jo971751v
日期:1998.7.1
A highly reactive, low-valent titanium (LVT) reagent has been prepared by the addition of substoichiometric amounts of iodine, to the LVT species generated by Rieke's method (TiCl3-Li-THF). While the conventional McMurry reaction requires high temperatures and prolonged reaction times for the generation of olefins, the present activated LVT reagent is able to effect the reductive coupling of aliphatic as well as aromatic carbonyls to the corresponding olefins at lower temperatures and much reduced reaction times. The protocol is also useful for the intramolecular coupling reactions leading to the one-step synthesis' of heterocycles. The temperature-controlled McMurry reaction provides enhanced diastereoselectivity and features an excellent chemoselectivity. In addition to the McMurry reaction, other SET-induced carbon-heteroatom (O, N) bond cleavages can also be carried out with the activated reagent at a fast rate and at a low temperature in high yields.
New Insights into the Mechanism of the McMurry Reaction
作者:Claude Villiers、Michel Ephritikhine
DOI:10.1002/anie.199723801
日期:1997.11.14
Not only pinacolate intermediates appear in McMurry reactions of aliphatic ketones R2CO (R = Me, Et, iPr) with MCl4Li(Hg) (M = Ti, U) [Eq. (1)]. Rather, carbenoid species must also be considered. This conclusion was drawn from an exact analysis of the reaction products as well as control experiments with pinacol derivatives.equation image
Titanium-induced reductive coupling of carbonyls to olefins
作者:John E. McMurry、Michael P. Fleming、Kenneth L. Kees、Larry R. Krepski
DOI:10.1021/jo00411a002
日期:1978.8
Synthesis of heavily substituted cyclopropylethylenes by titanium(0)catalyzed cross-coupling of ketones. Restricted rotation in 1,1-dicyclopropyl-2,2-di(2-propyl)ethylene