Alkenes Lithium 2,2,6,6-tetramethylpiperidide

Terminal epoxides 140 are deprotonated at 0°C using lithium tetramethylpiperidide (LiTMP). The resulting anion reacts with alkyl- and alkenylmagesium reagents under ring-opening. LiiO is eliminated and alkenes 141 are formed (equation 76) . ... 

Preparation of Cyclopropanes from Alkyl Halides. Alkenes, and Lithium 2,2,6,6-Tetramethylpiperidide... 

The second example is the deprotonation of an allyl monohalide at room temperature with lithium 2,2,6,6-tetramethylpiperidide in tetrahydrofuran in the presence of a tenfold excess of an alkene, directly leading to the vinylcyclopropane in 25-67% yield (see table below). ° The reaction takes place preferentially at the more substituted double bond. The eleetrophilic nature of the 2-methylpropenyl species was confirmed by a series of competition experiments. 

Trimethylsilylcarbene can be generated in solution via a-elimination (Method B) from (chloro-methyl)trimethylsilane with lithium 2,2,6,6-tetramethylpiperidide (LTMP) (see Houben-Weyl Vol. E19b, p 1412). " The generation of this carbene in the presence of an alkene leads selectively to the corresponding cyclopropane 9. Although the yields of the reactions with several cyclic or acyclic alkenes are rather modest (23-33%), these cyclopropanations proceed stereo-specifically and with high diastereoselectivity (Table 1). 

The products obtained from the reaction of (chloromethyl)trimethylsilane with organolithium reagents depend very much on the structure of the lithium compound. While lithium 2,2,6,6-tetramethylpiperidide initiates an a-elimination as described above, the treatment with sec-butyllithium leads to the formation of chloro(trimethylsilyl)methyllithium (11). This reagent cyclopropanates an electron-deficient alkene through sequential Michael addition and intramolecular ring closure (MIRC reaction), for example, the formation of cyclopropane 12. 

Reaction of Lithium 2,2,6,6-Tetramethylpiperidide with Substituted Benzyl Halides or 1-Chloromethylnaph-thalene in the Presence of an Alkene General Procedure 35... 

ALKENES Allyl dimethyldithiocarbamate. Bis(t -cyclopentadienyl)niobium trihydride. Cyanogen bromide. Di-n-butylcopperlithium. a,o-Dichloromethyl methyl ether. 2,3-Dimethyl-2-butylborane. N,N-Dimethyl dichlorophosphoramide. Diphenyl diselenide. Di-n-propylcopperlithium. Ferric chloride. Grignard reagents. Iodine. Lithium phenylethynolate. Lithium 2,2,6,6-tetramethylpiperidide. Methyl iodide. o-Nitro-phenyl selenocyanate. Propargyl bromide. rra s-l-Propenyllithium. Selenium. Tetrakis(triphenylphosphine)palladium. Titanium(IH) chloride. Titanium trichloride-Lithium aluminum hydride. p-Toluenesulfonylhydrazine. Triphenylphosphine. Vinyl-copper reagents. Vinyllithium. Zinc. 

Cyclopropane derivatives have been prepared using alkenes, cm-dihalides, and copper. This is a convenient and useful procedure, e.g. cis-cyclo-octene was converted into bicyclo[6,l,0]nonane (77%) and into a mixture of endo- and cxo-9-methoxy-carbonylbicyclo[6,l,0]nonanes (71 % exo. endo = 1.3 1) using di-iodomethane and methyl dibromoacetate, respectively. An improved procedure for the conversion of alkenes into cyclopropanols uses lithium 2,2,6,6-tetramethylpiperidide and 2-chloroethyl chloromethyl ether, e.g. cycloheptene was converted into the 2-chloro-ethyl ether of bicyclo[5,l,0]octan-8-ol (62% exo.endo = 1.8 1). ... 

A hindered Hthium amide such as lithium 2,2,6,6-tetramethylpiperidide (LTMP) has proved to be effective in triggering a direct intramolecular cyclopropanation of the unsaturated terminal epoxide 31 to the tricycHc alcohol 32 (2010JOC2157). This strategy has been used successfully in a concise synthesis of (—)-cubelol (33) from (—)-menthone. Similarly, the naturally occurring (—)-10-epicubelol (34) can be prepared from (+)-menthone. Interestingly, whatever is the stereochemistry of the tethered alkene, the facial selectivity of cyclopropanation is controlled solely by the epoxide stereochemistry (Scheme 8). 

---