With methyllithium to give olefins

Tosylhydrazones, formation, 52,122 with methyllithium to give olefins, 51, 69... 

Smaller cyclic olefins react with dibromocarbene to give the gem-dibromo-bicyclic systems, but these have not been reported to give allenes on reaction with methyl- or n-butyllithium. One possible reason may be the severe ring strain of cyclic allenes with less than seven carbon atoms. For example, Moore and Ward [14] found that 7,7-dibromobicyclo[4.1.0]heptane reacts with methyllithium to give bicyclic carbene intermediates which can be trapped with olefins (Eq. 4). 

After reprotection of the lactol, the resulting pentacyclic keto alcohol (271), was transformed into the corresponding tosylhydrazone, which was treated with excess methyllithium to give rise to olefin (272). 

Allenes are activated by a diphenylphosphine oxide substituent towards nucleophilic substitution at the j3-carbon atom. Lithium dimethyl-cuprate adds quickly to the 1,2-bond to give, on hydrolysis, the olefin in 16-84% yield, according to the nature of the substituents (76). Optimum conditions were not reported. The intermediate a-copper compound resulting from the addition can be dimerized or reacted with methyl iodide [Eq. (106)]. Similar reactions involving methyllithium are complicated. 

Alkyl-l,3,2-dioxaborinanes, prepared by asymmetric hydroboration of prostereogenic olefins with monoisopinocampheylborane and subsequent removal of the chiral auxiliary, react with methoxy(phenylthio)methyllithium followed by treatment with mercuric(II) chloride, to give a-methoxyalkyl derivatives. Oxidation of these intermediates in a pH 8 phosphate buffer provides x-chiral aldehydes (method ) which are transformed by further oxidation into the corresponding a-chiral acids (method ) and by reduction into /i-chiral alcohols (method )14. 

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]. 

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]... 

---