Aldehydes phenyllithium addition

The lower diastereoselectivity found with aldehyde 15 (R = CH3) can be explained by the steric influence of the two methyl substituents in close vicinity to the stereogenic center, which probably diminishes the ability of the ether oxygen to coordinate. In contrast, a significant difference in the diastereoselectivity was found in the additions of phenyllithium and phenylmagnesium bromide to isopropylidene glyceraldehyde (17)58 (see also Section 1.3.1.3.6.). Presumably the diastereo-sclcctivity of the phenyllithium addition is determined by the ratio of chelation-controlled to nonchelation-controlled attack of the nucleophile, whereas in the case of phenylmagnesium bromide additional chelation with the / -ether oxygen may occur. Formation of the -chelate 19 stabilizes the Felkin-Anh transition state and therefore increases the proportion of the anZz -diastereomeric addition product. 

The first use of chiral oxazolines as activating groups for nucleophilic additions to arenes was described by Meyers in 1984. " Reaction of naphthyloxazoline 3 with phenyllithium followed by alkylation of the resulting anion with iodomethane afforded dihydronaphthalene 10 in 99% yield as an 83 17 mixture of separable diastereomers. Reductive cleavage of 10 by sequential treatment with methyl fluorosulfonate, NaBKi, and aqueous oxalic acid afforded the corresponding enantiopure aldehyde 11 in 88% yield. 

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. 

However, with phenyllithium or phenylmagnesium bromide addition to arsenic takes preference to aldehyde addition 115). 

Other common, and commercially available, organolithium reagents include n-butyllithium and phenyllithium, and they react with both aldehydes and ketones. Note that addition to an aldehyde gives a secondary alcohol while addition to a ketone gives a tertiary alcohol. 

Treatment of (7 )-cinnamaldehyde (70) with an equivalent of phenyllithium in THF yields the enol (71), as expected. However, a number of other products are formed with an excess, including dihydrochalcone (72), the result of a tandem addition )3-alkylation. Observed concentration effects and variation of product distribution with reaction conditions, together with computational results, point towards a mechanism in which dimeric PhLi attacks the aldehyde without prior de-aggregation. ... 

The reaction of nonstabilized ylides with aldehydes can be induced to yield E-alkenes with high stereoselectivity by a procedure known as the Schlosser modification of the Wittig reaction. In this procedure, the ylide is generated as a lithium halide complex and allowed to react with an aldehyde at low temperature, presumably forming a mixture of diastereomeric betaine-lithium halide complexes. At the temperature at which the addition is carried out, fragmentation to an alkene and triphenylphosphine oxide does not occur. This complex is then treated with an equivalent of strong base such as phenyllithium to form a )8-oxido ylide. Addition of r-butyl alcohol protonates the P-oxido ylide stereoselectively to give the more... 

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