On the mechanism of the titanium-induced reductive coupling of ketones to olefins

Abstract

The reductive coupling of ketones, induced by low-valent titanium, was studied by using benzophenone and cyclohexanone as model compounds. The reaction conditions were optimized. It is essential that TiCl3 is reduced completely before addition of the ketone. The reaction mechanism is deduced from ESR measurements. Both the inorganic and organic part of the radical reaction are discussed. Various techniques were invoked to obtain a model for the actual coupling site. The coupling reaction occurs on the surface of an active titanium specimen.In the early seventies three groups of investigators2"4 established that low-valent Ti, prepared by the action of

The McMurry Coupling and Related Reactions

“…35 By contrast, ketyl radical intermediates have been detected by ESR in the reductive coupling of aromatic ketones with the TiCl 3 -Mg and TiCl 3 -LiAlH 4 reagent systems. 30 The ketyl radicals on titanium complexes are also produced by the reaction of aliphatic ketones and aldehydes with Ti(OSit-Bu 3 ) 3 , generated by the reduction of Ti(OSit-Bu 3 ) 3 Cl with Na(Hg). These have been characterized by ESR, although the radicals could not dimerize to form the pinacolates due to steric congestion.…”

“…However their oxidation states and structures have not been definitively identified. A zero-valent titanium species is proposed to be the active species in the coupling of ketones with the TiCl 3 -Li, K, or Mg system, 30 and a mixture of Ti(0), Ti(I), and Ti(II) with the TiCl 3 -LiAlH 4 system. 30 Conversely, it has been proposed that the McMurry coupling of ketones occurs on the ensemble of reduced titanium cations (+1, +2, and +3) on the TiO 2 (001) surface via the formation of pinacolate intermediates.…”

“…A zero-valent titanium species is proposed to be the active species in the coupling of ketones with the TiCl 3 -Li, K, or Mg system, 30 and a mixture of Ti(0), Ti(I), and Ti(II) with the TiCl 3 -LiAlH 4 system. 30 Conversely, it has been proposed that the McMurry coupling of ketones occurs on the ensemble of reduced titanium cations (+1, +2, and +3) on the TiO 2 (001) surface via the formation of pinacolate intermediates. 31 The active species for the practical coupling using the TiCl 3 -LiAlH 4 system has been isolated and characterized as [HTiCl(THF) 0.5 ] n (4) (Eq.…”

Reductive Coupling of Benzoic Acid Halides and Esters Using Low‐Valent Titanium

“…It leads to &-stilbene as the major product and to m -s t i l b e n e as the minor one, the latter compound being inert to further reduction under the reaction conditions (Table 2, run 9). Table 1, runs [13][14][15][16][17][18] show that the yield of tolane is high if the ratio Ti/PhCOCI is 2-3, but decreases at higher ratios. This is consistent with the results of Table 2, runs 1-3, which demonstrate that the reduction of tolane can be decreased by lowering the ratio Ti/tolane.…”

Konfigurations- und konformationsisomere paratrope, rotationsdynamische Tetraepoxy[32]annulene(6.2.6.2) und diatrope Tetraoxa[30]porphyrin(6.2.6.2)-Dikationen: Nachweis eines Tetraepoxy[31]annulen(6.2.6.2)-Radikalkations

“…The McMurry condensation of dialdehyde 6 yields the ( E,E,Z,E,E,E,Z )-4,5-dihydrotetraepoxy[32]annulene(6.2.6.2) (13a), where the configuration of the dialdehyde 6 ± beside the hydrogenated double bond ± is retained. As result of an intramolecular McMurry reaction of 6, (Z,E,Z,Z)-dioxa [16]annulene(6.2) 14 is formed. By oxidation of the [32]annulenes(6.2.6.2) 4a and 4b, a mixture of the four stereoisomeric tetraoxa [30]porphyrin(6.2.6.2) dications 5a/5a'/5b/5c is obtained; the configuration of the isomers is determined by COSY, NOESY, and NOE experiments.…”