Amide, ferf-butyl-, lithium

The reaction of ethyl A-arylcarbamates 3 with l-bromo-3,3-dimethyl-2-buta-none or l-bromo-3-ethyl-3-methyl-2-pentanone 4 in the presence of lithium bis(trimethylsilyl)amide (LiHMDS) results in the one-step synthesis of 3-aryl-5-ferf-butyl-2(3/T)-oxazolones 7 in fair to good yields (Fig. 5.2 Table 5.1, Fig. 5.3). This method is efficient for the preparation of bulky 5-substimted-2(37f)-oxazo-lones. 

Be this as it may, hthium attempts to bind to several bonding partners, and the structural consequences for the enolates of a ketone, an ester, and an amide are shown in Figure 10.2 In contrast to the usual notation, these enolates are not monomers at all The heteroatom that carries the negative charge in the enolate resonance form is an excellent bonding partner, such that several such heteroatoms are connected to every hthium atom. Lithium enolates often result in tetramers if they are crystallized in the absence of other hthium salts and in the absence of other suitable neutral donors. The hthium enolate of ferf-butyl methyl ketone, for example, crystallizes from THF in the form shown in Figure 10.3. 

Several new catalytic asymmetric protonations of metal enolates under basic conditions have been published to date. In those processes, reactive metal enolates such as lithium enolates are usually protonated by a catalytic amount of chiral proton source and a stoichiometric amount of achiral proton source. Vedejs et al. reported a catalytic enantioselective protonation of amide enolates [35]. For example, when lithium enolate 43, generated from racemic amide 42 and s-BuLi, was treated with 0.1 equivalents of chiral aniline 31 followed by slow addition of 2 equivalents of ferf-butyl phenylacetate, (K)-enriched amide 42 was obtained with 94% ee (Scheme 2). In this reaction, various achiral acids were... 

Enantioselective Claisen-type Acylation and Dieckmann-Type Annulation. To a solution of lithium TV-isopropyl-cyclohexylamlde (LICA) prepared from n-butyllithium and TV-isopropylcyclohexylamlne in THE was added dropwise a solution of ferf-butyl 2-phenylpropionate in THF at —78 °C under N2 with stirring. Hexamethylphosphoric triamlde (HMPA) was added and the mixture was stirred at —78 °C for 30 min. After addition of a solution of TV-acetyl (or A-butyryl) (, -IPTT amide in THF at —78 °C, the mixture was stirred at the same temperature... 

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