Peterson olefination methyllithium

However, the reaction of benzaldehyde with bis(trimethylsilyl)methyllithium gave a mixture of trans and cis isomers in a ratio of 1.4 1 (equation 128). If this reaction involved the /J-oxidosilane intermediate 158, the same stereochemical outcome would be expected. This was taken to suggest that, in this particular Peterson olefination reaction at least, the /J-oxidosilane 158 is not a major intermediate, and that the oxasiletane anion is formed directly by simultaneous formation of C—C and Si—O bonds. 

In reaction (28) y-elimination of LiCl with the formation of an epoxide is obviously faster than P-elimination of Me3SiOLi (Peterson-olefination). Seyferth and his collaborators34) found that this reaction takes place when bis(trimethylsilyl)bromo-methyllithium is reacted with carbonyl compounds, albeit not stereoselectively (Eq. (30)). In contrast, thermal dehydrohalogenation of 1,1-dichloro-l-phenyl-dimethylsilyl-alkanes furnishes Z-olefins only (Eq. (31)) according to the results of Larson et al. 35) ... 

Prepared by Peterson olefination from tris(trimethylsilyl)methyllithium and the corresponding aldehyde, see ref [39]. 

Bis(phenylsulfanyl)](trimethylsilyl)methyllithium and trimethylsilyloxirane do not afford a homo-Peterson reaction product, but a cyclopropane 4 a with a shifted phenylsulfanyl group. [Bis(phenylsulfanyl)](trimethylsilyl)methyllithium may be looked on as a carbenoid species which is in equilibrium with carbene and phenylsulfonate. This equilibrium may lie towards the carbanion. On addition of trimethylsilyloxirane, phenylsulfonate is trapped with formation of an alkoxide, which corresponds to the intermediate of a Peterson olefination of formaldehyde, and leads to phenyl vinyl sulfide. This provides a reaction partner for the liberated carbene giving cw-l,2-bis(phenylsulfanyl)-l-trimethylsilylcyclopropane (4a) in a stereospecific [2-1-1]... 

Segment C (21) is a relatively small molecule and is synthesized from 8. Acyclic stereocontrol for the construction of the C-29 chiral center was very important. Compound 8 was first converted to the lactone (22), which was treated with the carbanion of 23 to give 24. Removal of the sulfone with aluminum amalgam, spiro-ketalization, and Peterson olefination gave 25, which was treated with methyllithium at - 78 °C in tetrahydrofuran. Syn-addition controlled by an a-chelation occurred smoothly to give the expected segment C (21) in high yield [8a, b]. 

A homo-Peterson process intervened upon 1,4-rearrangement of the alkoxide formed by addition of tris(trimethylsilyl)methyllithium 124 to styrene oxide. The resulting carbanion 125 led mainly to the homo-Peterson product 126, with some of the adduct 127 from addition to a second equivalent of the epoxide. In their report, Fleming and co-workers noted that the homo-Peterson reaction is probably favored in this case by the benzylic positioning of the silyloxy group in 125, and they discussed the parallel between the Peterson olefination and a 1,3-Brook rearrangement process. ... 

Reaction of DMSB with triphenylsilyl-substituted oxiranyllithium leads to the formation of an olefinic silanol via sequential (1) coordination to the silicon, (2) Si-C bond migration, and (3) Peterson-type Si-O elimination to furnish the alkene. A pentacoordinate siliconate intermediate is presumably involved in this transformation. Therefore, it was reasonable to expect that addition of a nucleophile (methyllithium or lithium t>-propoxide) to an oxiranyl-substi-tuted SCB, which could generate a similar intermediate, would induce the C-Si bond migration to form the same silacyclopentane. Indeed, this alternative order of addition sequence provides the corresponding silanol with better efficiency (84% yield vs. 44%, Scheme 36). 

---