Synthetic applications of lithium

The preparation and some synthetic applications of lithium dialkylcuprates were described earlier (Section 14 11) The most prominent feature of these reagents is then-capacity to undergo conjugate addition to a p unsaturated aldehydes and ketones... 

The principal synthetic application of lithium dialkylcuprate reagents IS their reaction with a 3 unsatu rated carbonyl compounds Al kylation of the 3 carbon occurs... 

A review describing the major advances in the field of asymmetric reduction of achiral ketones using borohydrides, exemplified by oxazaborolidines and /9-chlorodiisopino- camphenylborane, has appeared. Use of sodium borohydride in combination with chiral Lewis acids has been discussed.298 The usefulness of sodium triacetoxyboro-hydride in the reductive amination of aldehydes and ketones has been reviewed. The wide scope of the reagent, its diverse and numerous applications, and high tolerance for many functional groups have been discussed.299 The preparation, properties, and synthetic application of lithium aminoborohydrides (LABs) have been reviewed. 

In this communication we wish to report results of our studies on the structure, some nucleophilic properties and selected synthetic applications of lithium dia 1kylcuprate adducts to various a,B-unsaturated organophosphorus compounds. 

An extension of the synthetic applicability of lithium halomethanes is achieved by the simultanous presence of another main group heteroatom at the same carbon. Thus, if one of the chlorine atoms of dichloromethyllithium is replaced by a sulfonylamin group, the following products are obtained by reaction with electrophiles (Eq. (23)) 25). The substituted carbenoid can be converted to normal carbonyl adducts as well as to olefins and cyclopropanes. 

Several chapters deal with the synthesis of and the synthetic applications of organolithium compounds such as orthometallation, arene catalysed lithiation, addition to carbon-carbon double bonds, their reaction with oxiranes, and asymmetric deprotonation with lithium (-)-sparteine. We gratefully acknowledge the contributions of ah the authors of these chapters. 

The synthetic applications of halocarbenoids are mainly determined by the framework bearing the carbenoid center. This article describes the different kinds of synthetic transformations that can be achieved by the use of alkylidene, a-heterosubstituted, cyclopropylidene, vinylidene, and allylidene lithium halocarbenoids. Their particuliar value in organic synthesis results from various rearrangement reactions of the primary adducts formed by reaction of the carbenoid with the electrophile. 

Since the preparative applications of lithium halocarbenoids have strongly increased in recent years, it is the purpose of this review to demonstrate the synthetic significance of these intermediates. 

In the addition reaction of cyanotrimethylsilane [147] to aliphatic aldehydes, another synthetic application of a BINOL-Ti catalyst was reported by Reetz [88]. In this instance, however, BINOL-TiCh was prepared by treatment of the lithium salt of BINOL with TiCU in ether (vide supra). The BINOL-TiCh thus obtained was used as a catalyst for the cyanosilylation reaction to give the cyanohydrins in up to 82 % ee (Sch. 62). 

A synthetic application of this cerium chloride methodology has been reported by Nagasawa et al., as shown in Schenne 25. It is noteworthy that aldol reaction of the cerium enolate proceeds in high yields, even though the acceptor carbonyl group is sterically crowded and is readily enolized by lithium enolates. 

The regiochemistry of deprotonation of imines derived from unsymmetrical ketones is of special significance for the synthetic applications of these anions for carbon-carbon bond formation. This selectivity is sensitive to both the amine moiety and the base used. With imines derived from cyclohexyl- or r-butyl-amine, deprotonation with either Grignard reagents or lithium dialkylamide bases will result in high selectivity (>98 2) for removal of the proton on the less substituted a-carbon as in equations (39) and (40). 3i... 

Virtually all of the synthetic applications of chiral dipole-stabilized organolithiums reported to date have the C— Li bond in an allylic or benzylic system. The most important consequence of this fact is that the two stereoisomers shown in Figure 3 can interconvert by pyramidal inversion. Therefore, the stereoselectivity of the deprotonation is irrelevant to the stereoselectivity as manifested in the product dia-stereomer ratio. The source of the selectivity in the organolithium alkylation step has not been determined. The available data do not permit a distinction between at least three possibilities thermodynamic control as determined by the equilibrating organolithium diastereomers, - kinetic control according to Curtin-Hammett kinetics,or increased carbon-lithium covalency at low temperature. ... 

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