Tetramethylpiperidide lithium, reaction with ketones

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

I-Alkynes from methyl ketones This reaction can be effected by conversion to Ihe enol phosphate followed by -elimination with LDA (equation I). In the case of a simple ketone such as 2-octanone the yield is low because of formation also of an allene. In such cases lithium tetramethylpiperidide is recommended as base. 

The dianions of /S-enamino ketones react with a wide range of electrophiles such as alkyl halides, oxiranes, nitriles, esters, aldehydes and ketones37. Dalpozzo and coworkers reported the generation of the dianion derived from /S-enamino ketones with lithium 2,2,6,6-tetramethylpiperidide and the reaction of the dianion with nitroalkene (Scheme 24)38. The dianion underwent exclusive alkylation at the y-carbon atom to give the monoalkylated product in high yield. This reaction is useful for the introduction of a nitro group into a ketone side chain. 

Aluminum enolates can be obtained also by transmetallation of lithium enolates (Scheme 31 ). 3 Diethylaluminum enolates can be produced regiospecifically through reaction of diethylaluminum chloride and zinc dust with a-bromo ketones and esters (Scheme 32). Obviously zinc is involved in this reaction, but the mild conditions are in sharp contrast to the Refoimatsky reaction and support the existence of an aluminum enolate in this process. The same type of enolate can be obtained from r-butyi acetates and diethylaluminum 2,2,6,6-tetramethylpiperidide (DATMP), which is generated in situ from diethylaluminum chloride and LITMP (Scheme 33). ... 

Control of Regioselectivity and Stereoselectivity. The recognition by Ireland and co-workers that Hexamethylphosphoric Triamide has a profound effect on the stereochemistry of lithium enolates has led to the examination of the effects of other additives, as the ability to control enolate stereochemistry is of utmost importance for the stereochemical outcome of aldol reactions. Kinetic deprotonation of 3-pentanone with Lithium 2,2,6,6-Tetramethylpiperidide at 0 C in THF containing varying amounts of HMPA or TMEDA was found to give predominantly the (Z)-enolate at a base ketone additive ratio of ca. 1 1 1, whereas with a base.ketone.additive ratio 1 0.25 1, formation of the ( )-enolate was favored (Table I). This remarkable result contrasts with those cases where HMPA base ratios were varied towards larger amounts of HMPA, which favored formation of the (Z)-enolate. ... 

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