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. 

Alkyl Grignard or phenyllithium addition to 31 affords 1-substituted... 

Alexakis et al. the used the combination of the diamine sparteine 1 (Scheme 4) with the Lewis acid BF3-OEt2 for phenyllithium additions to cyclohexene epoxide [Eq. (6)] [105]. They observed that addition of... 

Phenyllithium in ether adds to pyridazine and 6-substituted pyridazines at position 3. By using TMEDA, addition at position 4 is strongly promoted (78RTC116). 

The addition of phenyllithium to 6-arylpyridazin-3(2Er)-one takes place at position 6 to give 6-aryl-3-oxo-6-phenyl-l,2,3,4-tetrahydropyridazine and the reaction of 6-aryl-2,4-diphenylpyridazin-3(2H)-one with phenyllithium or phenylmagnesium bromide affords 6-aryl-2,3,4,6-pentaphenyl-l,2,3,4-tetrahydropyridazine (80S457). 

Aryl-2-phenyl-4,5-dihydropyridazin-3(2//)-ones react either with phenylmagnesium bromide or with phenyllithium to give 6-aryl-2,6-diphenyl-l,4,5,6-tetrahydropyridazin-3(2//)-ones (135) (products of 1,2-addition to the azomethine bond), while 2-methyl-6-phenyl-4,5-dihydropyridazine-3(2//)-one reacts with two equivalents of phenylmagnesium bromide at the carbonyl and azomethine group to produce 2-methyl-3,3,6,6-tetraphenyl-hexahydropyridazine (136) (Scheme 53) (80JPR617). 

In addition, there is a cleavage reaction whereby a perfluoroorgamc group is cleaved from a metal by a base, for example, phenyllithium [4], ethylmagnesium bromide [5], or a fluoride ion [6] (equations 3-5)... 

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. 

Alteration of the relative reactivity of the ring-positions of quinoline is expected and observed when cyclic transition states can intervene. Quinoline plus phenylmagnesium bromide (Et20,150°, 3 hr) produces the 2-phenyl derivative (66% yield) phenyllithium gives predominantly the same product along with a little of the 4-phenylation product. Reaction of butyllithium (Et 0, —35°, 15 min) forms 2-butylquinoline directly in 94% yield. 2-Aryl- or 6-methoxy-quinolines give addition at the 2-position with aryllithium re-agents, and reaction there is so favored that appreciable substitution (35%) takes place at the 2-position even in the 4-chloroquinoline 414. Hydride reduction at the 2-position of quinoline predominates. Reaction of amide ion at the 2-position via a cyclic... 

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 addition of phenyllithium to 3-hydroxy-l,3-diphenyl-1-butanone (4. R1 = R3 = C6HS R2 = H) leads to the predominant formation of either one or the other diastereomer, depending on the reaction temperature146. Thus, for this type of addition reaction there are at least two competing mechanisms which have quite different activation entropies147. 

The highest ee s reported to date for the addition of achiral organometallic reagents in the presence of aprotic chiral additives were observed with the C2-symmetric diamines 10, 11 and 12 (Table 25)13 — 15. Enantioselectivities as high as 89% ee were observed with chiral auxiliary 1012. Addition of phenyllithium to pentanal proceeds with lower enantioselection that the analogous addition of butyllithium to benzaldehydeu. Generally, the enantioselcctivity in-... 

The addition of a phenylcerium reagent 0 PhCeCl, ) in tctrahydrofuran to the pyrazoline 4 at — 78 C using an equimolar ratio of cerium(III) chloride, phenyllithium and pyrazoline (CcCI3/ Cf,H,I-i/4 1 1 1) exclusively provides the desired pyrazolidine 5 in good yields (75-94%). This product can be converted to the diamine 3a (R = H) and subsequently into numerous N-sub-stituted derivatives of 3a (e.g.. 3b R = CH3) by means of simple standard procedures23. 

Phenyllithium and phenylcopper boron trifluoride yield different diastereomers of the reaction products, i.c., the sense of asymmetric induction is a function of the metal. These results are rationalized on the basis of antiperiplanar 6 and synperiplanar 8 reactive enoate conformations for additions of the copper and lithium reagents, respectively. 

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. 

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