Propyne-, lithium

A solution of 0.21 mol of butyllithium in about 140 ml of hexane (note 1) was cooled below -40°C and 90 ml of dry THF ivere run in. Subsequently a cold (< -20 C) solution of 0.25 nol of propyne in 20 ml of dry THF was added with cooling below -20°C and a white precipitate was formed. A solution of 0.10 mol of anhydrous (note 2) lithium bromide in 30 ml of THF was added, followed by 0.20 mol of freshly distilled cyclopentanone or cyclohexanone, all at -30°C. The precipitate had disappeared almost completely after 20 min. The cooling bath was then removed and when the temperature had reached 0°C, the mixture was hydrolyzed by addition of 100 ml of a solution of 20 g of NHi,Cl in water. After shaking and separation of the layers four extractions with diethyl ether were carried out. The extracts were dried over magnesium sulfate and the solvents removed by evaporation in a water--pump vacuum. Careful distillation of the remaining liquids afforded the following... 

Note 1. Compare Chapter VIIl-6, Exp. 1 for the effect of lithium bromide on the formation of carbinols, derived from propyne. 

T rimethylsilylthio-1 -propyne from Lithium Propynethiolate and Trimethytchloro-silane... 

A heterogeneous mixture of lithium tribromodicuprate(I) (6.0 mmol), prepared by adding 2.4 mL (6.0 mmol) of a 2.5 M solution of dry lithium bromide in THF to 1.72 g (12.0 mmol) of copper(I) bromide in 2.5 mL of THF under nitrogen, is added to a solution of 5.0 mmol of l-methylsulfonyloxy-l-pbenyl-2-propyne (100% ee) in THF immediately after its preparation in situ as follows ... 

Reduction of 3-trimethyls1lyl-2-propyn-l-ol exemplifies the problem of stereoselectivity in hydride reduction of acetylenic alcohols to E-allyl alcohols.4 Early reports5 that lithium aluminum hydride stereoselectively reduced acetylenic alcohols gave way to closer scrutiny which revealed a striking solvent dependence of the stereochemistry. Specifically, the... 

Lithium, 157 a-Allenic Alcohols Methoxyallene, 177 3-Trimethylsilyl-1 -propyne, 329... 

The proper double-bond stereochemistry may be achieved by using 2-heptyne as a reactant in the final step. Lithium-ammonia reduction of 2-heptyne gives the trans alkene hydrogenation over Lindlar palladium gives the cis isomer. The first task is therefore the alkylation of propyne to 2-heptyne. 

It will be immediately clear from the boiling point of trimethylsilylpropyne (96 C at atmospheric pressure) that the use of a hexane solution of BuLi for the lithiation of propyne is not advisable. The best way is to metallate propyne with a solution of ethyllithium in Et20, prepared from C2HjBr and lithium. iJwy/lithium in Et70 would be less suitable, because of the formation of small amounts of octane (b.p. 128 C) during its preparation (Wiirtz-coupling). 

The Unusual Structures, Energies, and Bonding of Lithium-Substituted Allenes, Propynes, and Cyclopropenes. A. J. Kos, T. Clark, and P. v. R. Schleyer, Angeiv. Chem., 96, 622, (1984). Die ah Initio Berechnung der Struktur von 1,3-Dilithloaceton. 

Phenyl trimethylsilylpropargyl ether, (CH])3SiC=CCH20C6H5 (1). Mol. wt. 214.34. The ether is prepared by reaction of 3-phenoxy-l-propyne with n-butyl-lithium followed by chlorotrimethylsilane. 

Enantioselective Addition of Alkynyllithium to Aldehydes. The enantioselective addition of alkynyllithium to aldehydes in the presence of (1) provides optically active propargylic alcohols. (5)-l-Phenyl-2-propyn-l-ol with 92% ee is obtained in 87% yield from the enantioselective addition of Lithium (Trimethylsi-lyl)acetylide to PhCHO in the presence of (1) and the subsequent removal of the MesSi group (eq 3). "... 

The advantages of lithium acetylides over haloalkynes (in Michaelis-Arbuzov or Michaelis-Becker routes) have been clearly demonstrated in several comparable syntheses. For example, from tlie condensation of 3,3-diethoxy-l-lithio-l-propyne with diethyl chlorophosphate at -65°C, diethyl... 

The metalation of propyne in hexane was followed IR-spectroscopically by West He observed characteristic changes in the IR-spectrum with the stepwise introduction of lithium ... 

Starting with propyne itself (R , R R — H) even the last proton can be removed and the product CjLi may be called a sesquiacetylide 26 with both ligands of the sesquiacetylene 192 being replaced by lithium atoms o.-. ... 

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