Carbonate phenyllithium addition

The first example of asymmetric catalytic ring-opening of epoxides with sp2-hybridized carbon-centered nucleophiles was reported by Oguni, who demonstrated that phenyllithium and a chiral Schiff base ligand undergo reaction to form a stable system that can be used to catalyze the enantioselective addition of phenyllithium to meso-epoxides (Scheme 7.24) [48]. Oguni proposed that phenyllithium... 

The crystal structures of many organolithium compounds have been determined.44 Phenyllithium has been crystallized as an ether solvate. The structure is tetrameric with lithium and carbon atoms at alternating corners of a highly distorted cube. The lithium atoms form a tetrahedron and the carbons are associated with the faces of the tetrahedron. Each carbon is 2.33 A from the three neighboring lithium atoms and an ether molecule is coordinated to each lithium atom. Figures 7.2a and b show, respectively, the Li-C cluster and the complete array of atoms, except for hydrogen 45 Section 6.2 of Part A provides additional information on the structure of organolithium compounds. 

In Step H-7 the addition of phenyllithium to the cyclic carbonate group neatly generates the C(2) benzoate group. A similar reaction was used in several other Taxol syntheses. 

The above system failed entirely when nonstabilized carbanions such as ketone or ester enolates or Grignard reagents were used as carbon nucleophiles, leading to reductive coupling of the anions rather than alkylation of the alkene. However, the fortuitous observation that the addition of HMPA to the reaction mixture prior to addition of the carbanion prevented this side reaction1 extended the range of useful carbanions substantially to include ketone and ester enolates, oxazoline anions, protected cyanohydrin anions, nitrile-stabilized anions3 and even phenyllithium (Scheme 3).s... 

The ylide is prepared by deprotonating a triphenylalkylphosphonium salt with a strong base, commonly an organometallic base such as butyllithium or phenyllithium. The hydrogens on the carbon that is bonded to the phosphorus of the salt are somewhat acidic because the carbanion of the conjugate base (the ylide) is stabilized by the inductive effect of the positive phosphorus atom. In addition, a resonance structure with five bonds to phosphorus makes a minor contribution to the structure and provides some additional stabilization. The triphenylalkylphosphonium salt can be prepared by an SN2 reaction of triphenylphosphine with the appropriate alkyl halide (see Section 10.9). 

The primary site of attack in the reactions of the 1,2,5-thiadiazoles and selenadiazoles with lithium alkyls or Grignard reagents is usually at the ring sulfur or selenium (Scheme 2, path A) but attack on nitrogen (path B) or the ring carbon (path C) also occurs. yV-Phenyl-o-phenylenediamine is produced in the reaction of (1) and (2) with phenyllithium, probably via path B (55JCS1468). The driving force for this mode of addition could depend on the stable benzenoid character of the addition intermediate. 

The carbonyl carbon atom in the octahydro-l-pyrindones undergoes typical carbonyl addition reactions.142-147 For example, the cyanohydrin (213) is obtained from the corresponding oxo compound. Alcoholysis of 213 gives the ester.142 Phenyllithium adds smoothly to I,2-dimethyI-4-oxo-perhydro-l-pyrindine (207) to give 214.143-145... 

One of the first studies directed to carbon-carbon bond formation via Michael addition to a,p-unsatu-rated carbene complexes involved the examination of the traditional reagent for this purpose in organic systems. The reactions of the styryl complex (123) with phenyllithium and diphenyl cuprate were com-... 

The reaction of organolithium compounds with phenyl vinyl selenides proceeds by at least three different routes which involve (i) metallation, which leads to 1-phenyIseleno-l-vinylli-thium (Section 2.6.2.2.2) (ii) Se-Li exchange, which produces phenyllithium and a novel vinyl selenide (Scheme 104, or (Hi) addition of the organolithium across the carbon-cartx>n double... 

Activation of organolithium compounds. n-Butyllithium and phenyllithium react very slowly with diphenylacetylene. However, the 1 1 complex of either lithium compound and TMEDA reacts with diphenylacetylene at room temperature. For example, the reaction of /-butyllithium under these conditions followed by carbonation gives cis-4,4-dimethyl-2,3-diphenyl-2-pentenoic acid (1) and a trace of 2-phenyl-3-f-butylindone (2). Thus addition takes place as well as metallation.1... 

It might be expected that in the presence of TMEDA or other tertiary diamines anomalous reaction products might be obtained with organolithium compounds such as benzyllithium. A number of reports in the literature disclose instances of the expected reaction products from reactions such as carbonation to the carboxylic acid and addition to benzophenone (I, 3, 4, 12). The phenyllithium-TMEDA (1 1) complex in benzene was allowed to react with benzophenone to give a 95% yield of triphenylcarbinol and with cyclohexanone to yield 59% of the 1-phenylcyclohexanol. The reaction with excess trimethylsilyl chloride is apparently quantitative. The main consideration in using these complexes is to use low temperatures for reaction and aqueous washes of ammonium chloride solution in the work-up to remove all of the tertiary diamine (the odor can be detected in low concentrations.)... 

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