Lithiation oxygen-directed

Directed lithiations of a,3- and -y.b-unsaturated amides " have been extensively studied. Illustrative examples are shown in Scheme 44. Prior complexation of the alkyllithium base with the amide carbonyl oxygen directs the base to the thermodynamically less acidic -position in a,3-unsaturated amide (31), which adds to benzophenone and subsequently lactonizes. Analysis of the NMR spectrum reveals that the organolithium added the benzophenone in the equatorial position. A Afferent kinetic deprotonation is seen in y,8-unsaturated amide (32), where -lithiation to form an allylic anion predominates over a-lithiadon to form an enolate. > Addition of the lithium anion to acetone affords poor regioselectivity, but transmetalation to magnesium before carbonyl addition yields a species which adds exclusively at the 8-position. ... 

Propargylic ethers undergo directed lithiation and subsequent transmetallation to afford oxygenated allenyl titanium reagents. Subsequent addition of aldehydes gives rise to various homopropargylic alcohol adducts as mixtures favoring the anti dia-stereomers (Tables 9.18 and 9.19) [29, 30]... 

Figure 1. 7-LiJV[02 (layered) and 5-LiM204 (spinel) structures (M = 3d transition metal). M occupy octahedral sites in both structures. In 7-LiJV[02, M and Li (and/or vacancies) alternately occupy (111) planes of the ccp oxygen sublattice. The (111) plane parallel to the M layers is indicated by the black line between the layered and spinel structures. The [111] direction is shown as well. In s-Lii/2Mn02, (111) planes with three-fourths of the Mn alternate with (111) planes with one-fourth of the Mn. Li ions occupy tetrahedral sites in the planes with one-fourth of the Mn. The planes with three-fourths of the Mn are free of Li. In fully lithiated spinel-like 5-Li2Mn204, the Li move into octahedral sites. Three-fourths of the Li are in the (111) plane with one-fourth of the Mn, and one-fourth of the Li are in the plane with three-fourths of the Mn.

The lithiation of phenols protected as acetals—methoxymethyl acetals like 140 in particular—is especially valuable the second oxygen supplies a powerful coordination component to their directing effect (Scheme 69) The regioselective lithiation of 141 was used in the synthesis of the pterocarpans 4 -deoxycabenegrins A-I. 

Sulphoximinoferrocenes and ferrocenyl sulphonates can also be lithiated diastere-oselectively, with the sulphoximine oxygen atom of 358 directing the deprotonation. 

Lithiation and mercuration are directed by the oxygen atom and occur at the 4-position, but thallation, achieved by treatment of dibenzofuran with thallium(III) isobutyrate at 110°C, affords the 2-thallium di(isobutyrate), which may be converted to the 2-iodo compound by reaction with iodine. Mercuration is achieved by treatment of dibenzofuran with mercuryfll) acetate at 150°C, and the resultant 4-mercuric acetate (56%) may also be converted to the iodo compound. ... 

The reductive lithiation of cyclic benzofused ethers, for example, 510, with 4,4 -di-/< rt-butylbiphenyl (DTBB) and lithium gives intermediate organolithiums, for example, 511 and 512, that can be quenched with a variety of electrophiles to give general products 513 and 514 (Scheme 92). The process is not synthetically useful for 4H-chromene as carbon-oxygen bond cleavage occurs in both directions <2002TL4907>. 

A new method for the ortho hydroxylation of aromatic aldehydes via orrho-lithiated arcnnatic aminoal-koxides has recently been reported by Einhom et al Fonnation of the aminoalkoxide serves two purposes. Firstly, the aldehyde group is protected and, secondly, the aminoalkoxide directs lithiation to the ortho position. Oxidation of the lithio species was effected by either MoOPH or molecular oxygen, albeit in poor yield. Alternatively, a two-step, one-pot condensation of the lithio intermediate with tributyl borate followed by oxidation with hydrogen peroxide gave the ortho-hydroxy aldehydes (24) in slightly better yields (Scheme 9). 

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