Potassium compounds allylic halides

The 3-pyridyl Grignard reagent has been alkenylated by reaction with allyl halides and the 2-picolyl Grignard reagent homologated with alkyl halides and to-diethoxyalkyl halidesi . Of much greater importance has been the use of picolyl lithium, potassium and sodium compounds in reactions with alkyl and aralkyl halides. 

A series of tricyanomethyl compounds were prepared in refluxing acetonitrile hy alkylating potassium tricyanometha-nide with alkyl iodides, allyl, propargyl, and benzyl bromides. Yields of 20-57% were obtained for mono- and difunctional halides with a reflux time of 72 hours. The heats of combustion of these tricyanomethyl compounds as well as of two polycyano compounds were measured using a Dickenson-type calorimeter, and heats of formation were calculated with a precision of approximately 1.0%. From Pitzers values for C—C and C—H bond energies, that of the tricyanomethyl moiety is calculated to be about 810 kcal./mole, and the tricyanomethyl group is less stable than expected from comparison with AH°f of propylcyanide. 

The cross-coupling reaction of organoboron compounds with organic halides or triflates proceeds selectively in the presence of a base, such as sodium or potassium carbonate, phosphate, hydroxide, and alkoxide [11, 45], The bases can be used in aqueous solution, or in suspension in dioxane or DMF. In contrast, the cross-coupling reaction with certain electrophiles, such as allylic acetates [45], 1,3-butadiene monoxide [49], and propargyl carbonates [50], occurs under neutral conditions without any assistance from a base. The transmetallation of organoboron compounds with palladium halides under basic or neutral conditions can be considered to involve three routes, 1, 2, and 3 (Schemes 2-18, 2-20, and 2-23, below). 

As with preparing allyl complexes, direct reaction of benzyl halides and alkali metals is not a generally useful route to benzylalkali metal compounds due to R-R coupling. Benzylalkali metal compounds can be prepared by (1) addition of organometallic reagents to arylalkenes, (2) cleavage of benzyl ethers (equation 28), (3) transmetallation (equations 29-31), and (4) metallation of methyl substituted aromatics. Q, Q -Bis(trimethylsilyl)benzyl potassium can be prepared by metallation with a mixture of butyllithium and potassium 3-methyl-3-pentanolate in THF. ... 

This reaction was initially reported by Finkelstein in 1910. It is a preparation of alkyl iodide from alkyl bromide or chloride with potassium or sodium iodide in acetone. Therefore, this reaction is generally known as the Finkelstein reaction. Occasionally, it is also referred to as the Finkelstein halide exchange, Finkelstein displacement, or Conant-Finkelstein reaction. Mechanistically, this reaction is a simple nucleophilic substitution (often via Sn2), as iodide is a stronger nucleophile than bromide or chloride. The yield of this reaction is very high and can be quantitative if occurs in DMF. It was found that the trifluoromethyl group retards the displacement of bromide when it presents as an a- or /3-substituent but accelerates the reaction as a substituent in an allylic chloride. Under normal conditions, this type of halide displacement does not occur for aryl halides. For dihalides, unsaturated or cyclic compounds may form via carbocation intermediates, which form transient covalent iodides or are reduced directly by iodide to free radicals. However, the aromatic halide exchange reacts smoothly when 10% Cul is present in the reaction... 

If Ar = HiCO, a good yield of benzoyl cyanide is obtained. Allylic triphenyl-phosphonium halides react similarly with pentyl (isoamyl) nitrite and the products are decomposed by ethanolic potassium hydroxide to nitriles, for example, -methylcinnamonitrile is obtained in 57% yield and famesyl cyanide in 87% yield [127J. N-Nitroso compounds give nitriles on reaction with triphenylphos-phine alkylenes [128], for example... 

The regioselectivity (a vs. y) is controlledby many factors, such as the nature of the heteroatom, the base, the substituents bonded to the heteroatom, the electrophile, the solvent, and the reaction conditions. It has been proposed, as a rule of thumb, that for a given counter ion, e.g., lithium, anion-destabilizing substituents (e.g., OR, NR2) favor the attack by alkyl halides and protons at the y-position, while carbonyl compounds undergo reaction preferentially at the a-position. The complementary regioselectivity is encountered when anion-stabilizing substituents (e.g., SR, BR2) are bonded to the allyl moiety. A list of n-butyllithium/potassium ferf-butoxide metalated heterosubstituted alkenes is shown in Table 3. 

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