Tetramethylpiperidide lithium also

These reagents are not isolated but are used directly in reactions with aldehydes, after generation of ate complexes via the addition of an alkyllithium reagent or pyridine11. 2-(2-Propenyl)-1,3,2-dioxaborolane is also metalated upon treatment with lithium tetramethylpiperidide, but mixtures of a- and y-substitution products are obtained upon treatment of this anion with alkylating agents20. Consequently, this route to a-substituted allylboron compounds appears to be rather limited in scope. 

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 lithium enolate generated using lithium diisopropylamide [4111-54-0], lithium 2,2,6,6-tetramethylpiperidide [58227-87-1], or lithium hexamethyldisilazide [4039-32-17 is a chemical reagent that reacts with other reactants to give a variety of products (37). In the quest for improved stereospecificity, enolates with different cations such as silicon, aluminum, boron, and zinc have also been used (38). In group transfer polymerization, ketene silyl acetals, eg, (CH3)2C=C [OSi(CH3)3] (OCH3) are employed as initiators (39). 

Vinyl epoxides can also be ring-opened via an Sn2 sense, as exemplified in the macrocyclization of the epoxy-tethered cyclopentenone 76, which was induced to occur by treatment with lithium 2,2,6,6-tetramethylpiperidide (LTMP) followed by the mild Lewis acid diethylaluminum chloride in THF. The enolate attacked exclusively from the a-position of the... 

Acyclic bis(seleno)acetals 426 (R = H) must be deprotonated with LDA at —78 °C, because w-BuLi produces lithium-selenium exchange8,13,635 639. a-Lithioselenoacetals can also be prepared by this transmetallation from selenoorthoesters 427 (R = SeMe) with n-BuLi638,639. a-Alkyl substituted selenoacetals 426 (R = alkyl) can be deprotonated with LDA or lithium tetramethylpiperidide in the presence of HMPA at — 30 °C640. 

Carbonyl transposition. Yee and Schultz have used a modification of the method of Trost (8, 392) for this transposition. The first step also involves bissul-fenylation with this reagent, but more satisfactory results were obtained when the lithium enolate was generated with lithium tetramethylpiperidide. The remaining steps are formulated in equation (I). It is also possible to convert the intermediate hydroxy thioketal to the ketol, which is then mesylated and reduced to the trans-... 

The formation of 15 on treatment of 14 with lithium 2,2,6,6-tetramethylpiperidide is clearly a rearrangement of an allyl anion into a cyclopropyl anion, that is trapped by the electrophile iodomethane. However, since it is also an azacycloheptatriene to azanorcaradiene rearrangement, it will be covered in Section 2.3.2.1. 

The anion of 3-alkoxycarbonyl-3 f-azepines exhibits a reaction that is an allyl anion to cyclopropyl anion rearrangement (see Section 2.3.1.2.) and is also formally an azacyclohep-tatriene to azanorcaradiene rearrangement with an additional alkoxycarbonyl shift. Treatment of 13 (X-ray analysis) with lithium 2,2,6,6-tetramethylpiperidide (LTMP), followed by iod-omethane, provides 14 (X-ray analysis of picrate) in 50-60% yield. The mechanism as suggested by the authors is shown on the following page. 

Elimination followed by nucleophilic addition to a strained C-C double bond was the main reaction sequence observed when a 1 3 mixture of (2-bromo-5-methyltetracy-clo[3.2.0.0 . 0 ]hept-l-yl)methanol and (7-bromo-5-methyltetracyclo[3.2.0.0 .0 ]hept-l-yl)methanol was allowed to react with a large excess of lithium aziridide. The main product, identified as 2-(aziridin-l-yl)-5-methyltetracyclo[3.2.0.0 -. 0" ]hept-l-yl methanol (13) and isolated in 21% yield, most likely results from aziridide attack on the intermediate lithium 5-methyltetracyclo[3.2.0.0 .0" ]hept-2(7)-en-l-yl)methoxide at C2. ° The other main product, 3-(aziridin-l-yl)-l-methyl-4-oxatetracyclo[4.3.0.0 .0 ]nonane (14), which was isolated in 15% yield, conceivably originates from the same intermediate as outlined above. Acyclo-propene intermediate was probably also formed when l-chloro-5-methyl-exo-6-phenyl-3-oxabicyclo[3.1.0]hex-2-one reacted with lithium 2,2,6,6-tetramethylpiperidide (LTMP) and gave 5-methyl-e.vo-6-phenyl-l-(2,2,6,6-tetramethyl-l-piperidyl)-3-oxabicyclo[3.1.0]hex-2-one (15) in 66% yield. 

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