LiTMP

The analogous dimerization of alkynes over Fe(C0)5 is not applicable, so clearly a different route towards alkynylated derivatives of 25 was needed. Comparison of 25 to cymantrene suggests that metallation of the hydrocarbon ligand should be the route of choice for the synthesis of novel substituted cyclobutadienes. In the literature, addition of organolithium bases (MeLi, BuLi) to the CO ligands with concomitant rearrangement had been observed [25]. But the utilization of LiTMP (lithium tetramethylpiperidide, Hafner [26]) or sec-BuLi as effectively non-nucleophilic bases led to clean deprotonation of the cyclobuta-... 

Chelation affects the stereochemistry of enolate formation. For example, the formation of the enolates from a-siloxyesters is Z for LiHMDS, but E for LiTMP.19... 

The E.Z ratio can be modified by the precise conditions for formation of the enolate. For example, the E.Z ratio for 3-pentanone and 2-methyl-3-pentanone can be increased by use of a 1 1 lithium tetramethylpiperidide(LiTMP)-LiBr mixture for... 

Entry 2 shows an E-enolate of a hindered ester reacting with an aldehyde having both an a-methyl and (3-methoxy group. The reaction shows a 13 1 preference for the Felkin approach product (3,4-syn) and is controlled by the steric effect of the a-methyl substituent. Another example of steric control with an ester enolate is found in a step in the synthesis of (-t-)-discodermolide.99 The E-enolate of a hindered aryl ester was generated using LiTMP and LiBr. Reaction through a Felkin TS resulted in syn diastereoselectivity for the hydroxy and ester groups at the new bond. 

An unusual domino process was observed by Biehl and coworkers [69] in the reaction of 2-bromo-l-naphthol 4-196 with arylacetonitriles in the presence of LDA or LiTMP by employing 3-thienylacetonitrile 4-197, the tetracyclic compound 4-200 was obtained in 57% yield (Scheme 4.43). The reaction probably includes the formation of an aryne and a ketenimine which undergo [2+2] cycloaddition to give 4-198, followed by rearrangement and allylic addition to the intermediately formed aryl cyano compound 4-199. 

The easily obtainable 1,2-dihydro-2-boranaphthalene 27 can be depro-tonated by lithium 2,2,6,6-tetramethylpiperidide (LiTMP) to give the 2-boratanaphthalene 28, characterized via its derivative 29 (Scheme 5) (26). 

Only few general methods allow for the introduction of a substituent at the C-7 position. However, treatment of cyano-enamide 335 with LiTMP followed by reaction with electrophiles has been successfully used to introduce an alkyl chain at G-7. It is worth noting that the amide obtained by acidic hydrolysis of the cyano-enamide group can be further alkylated to form tricyclic hexahydro-oxazolo[3,2- ]pyridin-5-ones 337 (Scheme 92) <1998JOC1619>. 

Generation in situ. Butyllithium (primary, secondary, or tertiary) can be generated by sonication of a mixture of lithium wire and a butyl chloride at 15° in dry THF. The corresponding butane is evolved under these conditions and LiCl precipitates the reaction is generally complete within 15 min. The highly useful lithium diisopropylamide can be prepared by sonication of a mixture of diisopropylamine, lithium, and butyl chloride in dry THF or ether. The yield is 91% and the solution can be used directly for deprotonation. Other lithium amides, even LiTMP, can be prepared in the same way. 

This was the first-described, non-stabilized ylide, obtained by treatment of the corresponding telluronium tetrafluoroborate with hthium 2,2,6,6-tetramethylpiperidide (LiTMP). Epoxides are obtained by reaction with both aldehydes and ketones. ... 

Reaction of telluronium methylide with carbonyl compounds (general procedure A solution of LiTMP (1.2 mmol) in THF is added to a solution of diphenyltelluronium methyl tetrafluoroborate (1.2 mmol) in THF (8 mL) at -78°C under Nj. The mixture is warmed to -70°C and stirred for 30 min. After cooling to -78°C, the carbonyl compound (1.0 mmol) in THF (2 mL) is added. The reaction mixture is then allowed to warm at room temperature. After the reaction is complete (monitored by TLC), the usual work-up and flash chromatography gives the product. 

As in the preceding case, the ylide is obtained using LiTMP as the base and gives epoxides with aldehydes and ketones. z... 

---