Structure organolithium reagents

The asymmetric addition of organolithium reagents to arylox azolines has been used to construct highly complex polycyclic terpene structures found in natural products. For example, the asymmetric addition of vinyllithium to chiral naphthyloxazoline 3 followed by treatment of the resulting anionic intermediate with iodoethyl dioxolane 61... 

The first stable silaallene, 56, was synthesized in 1993 " " by the intramolecular attack of an organolithium reagent at the /f-carbon of a fluoroalkynylsilane (Scheme 16). Addition of two equivalents of r-butyllithium in toluene at O C to compound 54 gave intermediate 55. The a-lithiofluorosilane then eliminated lithium fluoride at room temperature to form the 1-silaallene 56, which was so sterically hindered that it did not react with ethanol even at reflux temperatures. 1-Silaallene 56 was the first, and so far the only, multiply bonded silicon species to be unreactive toward air and water. The X-ray crystal structure and NMR spectra of 56 is discussed in Sect. IVA. 

Sulfur diimides react quantitatively with organolithium reagents at the sulfur centre to produce lithium sulfinimidinates of the type Li[RS(NR )2] A. The lithium derivatives may be hydrolysed by water to R NS(R)NHR which, upon treatment with MH (M=Na, K) or the metal (M=Rb, Cs) in THF, produces the heavier alkali-metal derivatives.132 The structures of these complexes are influenced by (a) the size and electronic properties of the R group, (b) the size of the alkali metal cation, and (c) solvation of the alkali-metal cation. 

The use of sterically hindered secondary organolithium reagents, such as (CgH jCH Li, drastically favors the O-alkyl scission of thejbster group (37) finally, organolithium compounds leading to non enolizable keto functions in the first step of substitution, such as C H Li, promote competitive and consecutive reactions resulting in complex copolymers of poorly defined structure (38,39) ... 

Two-dimensional 6Li/Y correlation spectra of organolithium reagents have been studied for some time and although in previous reports a variety of elements such as 31P, 29Si, and 7Li11,82 have been employed as the heteronucleus Y, recent studies focused essentially on the application of 6Li/13C and 6Li/15N correlations for the structural investigation of lithium amides and lithium organyls, respectively. Methods employed include... 

Experimental mechanistic studies of such reactions are in their early days. However, it is clear that proper understanding will rely on the prior isolation of the organolithium reagent, rather than on its production, then use, in situ. Thereafter, the reagent needs to be identified (e.g., RLi or RLi xL ) and characterized structurally, in the solid by X-ray diffraction and, perhaps more importantly, in solutions (by colli-gative molecular mass measurements and multinuclear NMR spectroscopic studies) in which it will be used. 

Several asymmetric 1,2-additions of various organolithium reagents (methyllithium, n-butyllithium, phenyllithium, lithioacetonitrile, lithium n-propylacetylide, and lithium (g) phenylacetylide) to aldehydes result in decent to excellent ee% (65-98%) when performed in the presence of a chiral lithium amido sulfide [e.g. (14)], 75 The chiral lithium amido sulfides invariably have exhibited higher levels of enantioselectivity compared to the structurally similar chiral lithium amido ethers and the chiral lithium amide without a chelating group. 

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