Lead-carbon bonds lithium metal

Treatment of substituted phthalans 1172 with lithium metal in the presence of catalytic quantities of naphthalene leads to reductive cleavage of the arylmethyl carbon-oxygen bond to form a stable dilithium compound 1173, which upon trapping with carbon dioxide furnishes isochroman-3-ones 1174 (Scheme 289) <1996JOC4913>. 

Mixed bimetallic reagents possess two carbon-metal bonds of different reactivity, and a selective and sequential reaction with two different electrophiles should be possible. Thus, the treatment of the l,l-bimetailic compound 15 with iodine, at — 78"C, affords an intermediate zinc carbenoid 16 that, after hydrolysis, furnishes an unsaturated alkyl iodide in 61% yield [Eq. (15) 8]. The reverse addition sequence [AcOH (1 equiv), —80 to — 40 C iodine (1 equiv)] leads to the desired product, with equally high yield [8]. A range of electrophile couples can be added, and the stannylation of 15 is an especially efficient process [Eq. (16) 8]. A smooth oxidation of the bimetallic functionality by using methyl disulfide, followed by an acidic hydrolysis, produces the aldehyde 17 (53%), whereas the treatment with methyl disulfide, followed by the addition of allyl bromide, furnishes a dienic thioether in 76% yield [Eq. (17) 8]. The addition of allylzinc bromide to 1-octenyllithium produces the lithium-zinc bimetallic reagent 18, which can be treated with an excess of methyl iodide, leading to only the monomethylated product 19. The carbon zinc bond is unreactive toward methyl iodide and, after hydrolysis, the alkene 19... 

The Grignard reagent is the best-known member of a broad class of substances, called organometallic compounds, in which carbon is bonded to a metal lithium, potassium, sodium, zinc, mercury, lead, thallium—almost any metal known. Each kind of organometallic compound has. of course, its own set of properties, and its particular uses depend on these, fiut, whatever the metal, it is jess electronegative than carbon, and the carbon-metal bond—like the one in the... 

Benzyl phenyl sulfides can be sequentially metallated and alkylated. The cleavage of the carbon-sulfur bond in the resulting product leads to a benzyllithium and lithium phenylthiolate. Alkylation of the former organometallic then produces an alkylbenzene (Scheme 15), but competing alkylation on the thiolate is however observed. 

The nature of the carbon-metal bond varies widely, ranging from bonds that are essentially ionic to those that are primarily covalent. Whereas the structure of the organic portion of the organometaiiic compound has some effect on the nature of the carbon-metal bond, the identity of the metal itself is of far greater importance. Carbon—sodium and carbon-potassium bonds are largely ionic in character carbon—lead, carbon—tin, carbon—thallium, and carbon—mercury bonds are essentially covalent. Carbon—lithium and carbon—magnesium bonds lie between these extremes. 

Alkyllithium compounds as well as polymer-lithium associate not only with themselves but also with other alkalimetal alkyls and alkoxides. In a polymerization initiated with combinations of alkyllithiums and alkalimetal alkoxides, dynamic tautomeric equilibria between carbon-metal bonds and oxygen-metal bonds exist and lead to propagation centers having the characteristics of both metals, usually somewhere in between. This way, one can prepare copolymers of various randomness and various vinyl unsaturation. This reaction is quite general as one can also use sodium, rubidium or cesium compounds to get different effects. 

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