Remarkable Effect of Fullerenes on Low-Valent Titanium Mediated Organic Reaction

Talukdar, Sanjay; Nayak, Sandip K.; Banerji, Asoke

doi:10.1080/153638x9508543787

Cited by 9 publications

(15 citation statements)

References 7 publications

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“…Because of the existence of a definite Ti−Mg bond in [ A ], Ti is likely to assume higher electron density (compared to metallic Ti) when one considers the more electropositive character of Mg. This might also explain our earlier observation of higher reactivity of TiCl 3 /Li/THF in the reductive dealkoxylation of aryl alkyl ethers,17a because of the higher electropositivity of Li as compared to that of Mg in TiCl 3 /Mg/THF system.…”

Section: Resultsmentioning

confidence: 58%

“…Reductive Coupling of Acetophenone by Pyridine-Modified Low-Valent Titanium Reagent. Based on our earlier work on the effect of various nitrogenous bases on the reactivity of LVT reagent for dealkoxylation of aryl alkyl ethers,17b pyridine was selected for the present studies on account of its high efficacy and easy availability. The LVT generated from TiCl 3 and 1.5 equiv of Mg metal in THF was treated with increasing amounts of pyridine, keeping a constant THF-volume.…”

Section: Resultsmentioning

confidence: 99%

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Influence of External Ligands and Auxiliaries on the Reactivity of Low-Valent Titanium in McMurry Reaction: Selectivity and Mechanistic Profile

1996

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Influence of various external ligands/auxiliaries on the reductive carbonyl coupling reactions mediated by low-valent titanium (LVT) reagents (McMurry coupling) has been explored. The LVT species generated from Tyrlik's TiCl3−Mg−THF system has been selected for the reactivity-tuning trials. Our studies show that incorporation of about 10 equiv of pyridine (a π-acceptor ligand) with respect to TiCl3 to the THF solvated LVT reagent could arrest the reductive dimerization of acetophenone at the intermediate pinacol stage. Modulation of the LVT-species by covalently-binding monohydroxy, 1,2- and 1,3-dihydroxy auxiliaries also resisted deoxygenation completely to give the pinacols in higher yields and better diastereoselectivity, as compared to pyridine-modified LVT system. Amongst these modified reagents, the LVT−catechol (1:1) system was found to be the most efficient combination for total pinacolization of aromatic carbonyl compounds, even under refluxing conditions. The actual titanium reagent responsible for this transformation is proposed to be a Ti(II) complex formed in situ. Further enhancement of stereoselectivity (threo-selectivity) of the pinacols has been achieved by carrying out the reactions with LVT-complexes modified by a variety of covalently-linking auxiliaries at low temperatures. The results demonstrate that by the judicious incorporation of various ligands/auxiliaries into LVT reagents it is possible to widen the scope and applicability of the classical McMurry reaction.

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Section: Resultsmentioning

confidence: 58%

Section: Resultsmentioning

confidence: 99%

Influence of External Ligands and Auxiliaries on the Reactivity of Low-Valent Titanium in McMurry Reaction: Selectivity and Mechanistic Profile

1996

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“…In contrast, using 1,2-dibromoethane, 3a (87%) was obtained after 5 h reaction (Table , entry 8). The diol 2a was obtained as a diastereomeric ( dl : meso ) mixture (Table , entries 2 and 7), and their stereoisomeric composition has been assigned by comparison with the literature data 2d. The profile of the McMurry reaction using various additives as activators for LVT reagents establishes that TiCl 3 −Li−THF−I 2 (0.25 equiv) (LVT−I 2 , reagent B) is the best combination and, therefore, was used for further studies.…”

Section: Resultsmentioning

confidence: 99%

“…The products were fully characterized by comparison (TLC, mp, 1 H NMR, IR) with authentic samples. 2d, b Ratios determined by 1 H NMR analysis of crude product mixtures. c Stereochemical assignments are made by comparison of spectroscopic data to that reported in the literature 2d. The stereoisomeric composition of stilbene mixture 3a is presented in Table .…”

Section: Resultsmentioning

confidence: 99%

“…For the transition-metal-based reagents in general, and for low-valent titanium (LVT) in particular, it is widely known 1a-d that the reactivity, reproducibility, and stereochemistry of reaction products vary greatly with the source of the metal, its method of preparation, and the experimental conditions. In a continuation of our work on the rational design of organometallic reagents, 1b,2a-e fine-tuning of the reactivity of LVT was achieved by using external ligands, including π-acid species such as pyridine, triphenylphosphine, and fullerenes. Very recently, the ligand effects on the McMurry pinacol reactions have been examined .…”

Section: Introductionmentioning

confidence: 99%

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Activation of Low-Valent Titanium Reagents with Iodine: Facile Low-Temperature McMurry Reaction and N/O-Debenzylation/Deallylation

1998

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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.

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The McMurry Coupling and Related Reactions

Takeda

Tsubouchi

2013

Organic Reactions

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The McMurry coupling reaction has been recognized as one of the most efficient methods for the synthesis of alkenes from carbonyl compounds. This reaction can be applied to the preparation of various alkenes that are otherwise difficult to prepare. For example, sterically congested tetrasubstituted alkenes as well as medium to large membered rings involving natural products may be accessed via this process. This coupling utilizes various low‐valent titanium reagents generated by the reduction of titanium (III or IV) chloride with K, Zn, LiAlH 4 , C 8 K, amongst others. Furthermore, a variety of low‐valent metal species other than titanium, including aluminum, zirconium, niobium, molybdenum, indium, tungsten, and samarium, have also been found to promote the reductive coupling of carbonyl compounds. The scope and limitations of these reagent systems are reviewed in this chapter, together with the stereochemistry and reaction mechanism. This reaction is categorized into four coupling modes: i) homocoupling giving symmetrical alkenes, ii) mixed coupling giving unsymmetrical alkenes, iii) intramolecular coupling giving cycloalkenes, and iv) tandem coupling giving cyclic polyenes. Characteristics of these reaction modes are described briefly. A selection of synthetic applications are reviewed, including examples of the preparation of sterically congested and strained alkenes, medium to large‐ring compounds, biologically active targets, as well as substrates applicable in material science. Experimental conditions used for this versatile process are summarized to assist the choice of suitable conditions.

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Remarkable Effect of Fullerenes on Low-Valent Titanium Mediated Organic Reaction

Cited by 9 publications

References 7 publications

Influence of External Ligands and Auxiliaries on the Reactivity of Low-Valent Titanium in McMurry Reaction: Selectivity and Mechanistic Profile

Influence of External Ligands and Auxiliaries on the Reactivity of Low-Valent Titanium in McMurry Reaction: Selectivity and Mechanistic Profile

Activation of Low-Valent Titanium Reagents with Iodine: Facile Low-Temperature McMurry Reaction and N/O-Debenzylation/Deallylation

The McMurry Coupling and Related Reactions

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