Lithium amides transmetallation reactions

Potassium amides (NHR or NRR ) are generally produced via one of three synthetic routes (a) transmetallation of lithium amides with KOBu (b) reaction of KN(SiMe3)2 or (c) reaction of K, KH, KBu or KBz with an amine. 

Scheme 3.1 Transmetallation reactions of magnesium bromide with a range of lithium amides and neutral donors ...

Non-aromatic organolithium compounds can be prepared by transmetallation of resin-bound stannanes [25] or by deprotonation of alkynes [26], triphenylmethane [27], or other resin-bound C II acidic compounds with lithium amides or similar bases (Figure 4.3). The reaction of polystyrene-bound trialkylboranes with diethylzinc yields resin-bound alkylzinc derivatives [28]. 

Transmetallation is also appropriate for creating boron-nitrogen bonds. Starting from molecules containing (acidic) NH functions, the nitrogen atom is readily metallated by n-butyl lithium. Subsequent reaction of the lithium amide with a suitable element halide provides the desired precursor, while the lithium halide is eliminated (Eq. 5) [25, 27] ... 

The first amido-NHCs were reported by Arnold et al in 2003. The ligand preeursor could be eonveniently deprotonated with n-BuLi or LiN". The corresponding lithium amide bromide adduct reacted in a transmetallation reaction with a variety of homoleptic rare earth amides. Later, the Arnold group reported a series of rare earth complexes coordinated with this type of ligand (Scheme 6.5). ... 

Synthesis of 4,4 -(5-cyanobenzene)-l,3-bis[l,2,3,5-diselenadiazolyl] 28 was reported (Scheme 53) <1993CM820>. The starting material, 5-cyanobenzene-l,3-bis[iV,iV,iV1-tris(trimethylsilyl)carboxamidine] 329, was prepared by treatment of 1,3,5-tricyanobenzene 328 with 2equiv of lithium bis(trimethylsilyl)amide, followed by transmetalation with trimethylsilyl chloride. Reaction of the bis(amidine) 329 with 4 molar equiv of SeCh affords the bis(l,2,3,5-diselenadiazolium) dication as its dichloride salt [28][Cl2]. Reduction of the dication with triphenyl-antimony affords compound 28 in 26% from the bis(amidine) 329. 

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. 

Most metal enolates are generated by transmetalation from Li enoiates. However, Ti-enolates can be formed by action of TiCiyz -PrjNEt on carbonyl confounds [404,1042] and Zr-enolates can be generated by similar reactions with Zr(0-/ert-Bu)4 [1245], Lithium E-endates are obtained by deprotonation of ketones or esters with a branched Li-amide (LDA, LICA, LOB A, LTMP) in a weakly polar medium (THF or THF-hexane), while Z-enolates are formed by using LDA or LHMDS in the presence of HMPA or DPMU [1016], Tertiary amides always give Z-endates, and difunctionalized derivatives such as Evans s oxazolidinones 5.30 and 5.31 are chelated to the metal prior to enolization. 

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