Transmetallation mercury-lithium

In the initial studies about the reaction of /V.zV-disubstituted formamides with alkaline metals to give glyoxylic amides, the participation of carbamoyl metal derivatives as intermediates was postulated83. The first preparation of the carbamoyllithium 77 was described two years later by a mercury-lithium transmetallation from compound 76 at —75 °C (Scheme 20)84. The authors proposed also an aminocarbene structure 78 and studied its reactivity with methanol, methyl iodide, carbonyl compounds, esters, acyl chlorides, mercury(II) chloride and tri-n-butyltin chloride providing compounds 79. 

Aminomercurated olefins also undergo mercury-lithium transmetallation to give the dianions (8), which react with a variety of electrophiles to give substituted secondary arylamines (Scheme 15). o-Alkylated arylamines are the products of the reaction of arylaminodivinylboranes with acetylene derivatives."... 

Vinyl selenides have been lithiated at the a-position by LDA983,984 at —78 °C in THF to give a-(arylselanyl)vinyllithiums 680, a-(methylselanyl)vinyllithiums 681 being obtained by selenium-lithium transmetallation from l,l-bis(methylselanyl)alkenes with n-BuLi in THF or t-BuLi in ether at —78 °C985 986. These intermediates reacted with alkyl halides, epoxides, carbonyl compounds and DMF985, the final deprotection being performed by mercury(II) salts986. 

Transmetalation with rert-butyllithium, however, is not always the better way to achieve mercury-lithium exchange reactions. Although we had no problems with the... 

Transmetalation using tin-lithium exchange is an excellent method — even better than mercury-lithium exchange — for the preparation of organolithium compounds, but it works only for compounds being more stable than n-butyllithium. This is also true for the synthesis of polylithiumorganic compounds. Examples are ( , )-1,5-dilithio-1,4-pentadiene 99the (Z,Z)-l,5-dilithio-l,4-pentadiene derivative 101 —... 

Alkynyllead triacetates can be prepared by tin-lead or by mercury-lead exchange.88,8811 However, more convenient methods were subsequently devised. In situ transmetallation can be directly realized by lithium-lead or zinc-lead exchange. This avoids the isolation of unstable alkynylmetal derivatives. Ikegami et al. found that, if a THF solution of... 

Butyllithium is the reagent of choice for effecting a number of transmetalation reactions involving the replacement of tin, selenium, tellurium, or mercury by lithium. These reactions... 

Lithium 2,2,6,6-tetramethylpiperididejmercuric chloride o,o -Disubstitution via lithium-mercury transmetalation... 

Vinyl complexes are typically prepared by the same methods used to prepare aryl complexes. Vinyl mercury compounds, like aryl mercury compoimds, are easily prepared (by the mercuration of acetylenes), and are therefore useful for the preparation of vinyl transition metal complexes by transmetallation. The use of vinyl lithium reagents has permitted the s rnthesis of homoleptic vinyl complexes by transmetallation (Equation 3.35). Reactive low-valent transition metal complexes also form vinyl complexes by the oxidative addition of vinyl halides with retention of stereochemistry about the double bond (Equation 3.36). Vinyl complexes have also been formed by the insertion of alkynes into transition metal hydride bonds (Equation 3.37), by sequential electrophilic and nucleophilic addition to alkynyl ligands (Equation 3.38), and by the addition of nucleophiles to alkyne complexes (Equation 3.39). The insertion of alkynes into transition metal alkyl complexes is presented in Chapter 9 and, when rearrangements are slower than insertion, occurs by s)m addition. In contrast, nucleophilic attack on coordinated alkynes, presented in Chapter 11, generates products from anti addition. 

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