Alkylation, -hydroxyketones Carbonyl

Regiospecific and enantioselective aldol reactions 168) were also performed with SAMP (137). Lithiated hydrazones obtained from ketones (154) as described above were alkylated with carbonyl compounds and the adducts then treated with chloro-trimethylsilane. The resulting trimethylsilylethers (155) were finally oxidatively hydrolyzed to yield the chiral (3-hydroxyketones (156) (e.e. = 31-62%)168),... 

A catalyzed alcohol reaction (b) on lignin takes place at -hydroxyketones, carbonyl, and carboxyl groups. The reactions give different products and are shown in equation 3. Since alcohol/acid alkylation does not alkylate the aromatic hydroxyl groups (108), alkyllignins fiom these reactions have sharply different solubility... 

There are two approaches to lithium derivatives of aldehydes, though neither starts from the aldehydes themselves. Carbonylation of primary alkyl-lithiums gives an intermediate,4 probably 8, that adds to aldehydes or ketones, e.g. 9, to give hydroxyketones 10 and can be silylated to give the acyl silane 11. 

The asymmetric Michael addition of nonstabilised ketone enolates has proved difficult, with most success achieved using 1,3-dicarbonyls as donors. However, Shibasaki and coworkers have achieved high ees in the addition of a-hydroxyketones with both aromatic Michael acceptors such as (11.32) and also cyclic enones and alkyl vinyl ketones, using bifiinctional zinc catalysts prepared from linked BINOL (11.33). These catalysts are also effective in the asymmetric aldol reaction (see Section 7.1) and incorporate two zinc atoms, one of which activates the acceptor carbonyl group and the other forms a zinc enolate with the donor. In addition, catalysts of this type have been used to good effect in the addition of P-ketoesters to cyclic enones. 

The method could be applied to reduce 1,3-diaryl-1,3-diketones to 1,3-diaryl-1,3-propanediols in 93-100% yields and high ee s (>97% ee). The products were obtained as a mixture of diastereomers (81 19 - 90 10) and could be purified by recrystallization.Symmetrical 2-substituted-l,3-diaryl-1,3-diketones underwent reductive desymmetrization to give rise to /8-hydroxyketones (45-97% yields) in high ee s (>91% ee) and diastereoselectivities (dr>99 l) (eq 32). Unsymmetrical 2-alky 1-3-ary 1-1,3-diketones were reduced chemoselectively at the aryl-substituted carbonyl group to yield 2-alkyl-3-aryl-3-hydroxyketones (41-48% yields) in high ee s (>95%) and diastereoselectivities (( >97 3). The yields could be further improved by the addition of a stoichiometric amount of sodium methoxide in a one-pot reaction. 1,4-Diaryl-1,4-butanediones were reduced to enantiopure l,4-diaryl-l,4-butanediols (60-100% yields), which... 

These, too, are nucleophilic species that, after alkylation, can be converted to ketones. For example, a-hydroxyketones are formed when the lithioaldimine adds to a carbonyl group ... 

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