Alkynyl-lithium compound

Scheme 16). This regioisomer is also obtained in appreciable amounts if bulky lithium organometallies are used. Intramolecular carbolithiations have been reported, such as the cyclization of 5-alkynyl-lithium compounds to furnish the cyclized products in low yields.3... 

The degree of aggregation of organolithium compounds (alkyl-, aryl-, and alkynyl-lithium compounds as well as lithium enolates) in dilute tetrahydrofuran solution at —108 °C has been determined by means of cryoscopic [289] and NMR spectroscopic measurements [290] for a review on the solution structure of Hthium enolates and phenolates, see reference [406]. 

From alkynyl Grignard and lithium compounds and organyl tellurenyl halides... 

Alkenyl, alkynyl, and aryl halides, like alkyl halides, can be converted to the corresponding magnesium and lithium compounds. However, the reaction conditions, such as choice of solvent, can be critical. Bromoethene, for instance, can be converted to ethenylmagnesium bromide in good yield if the solvent is oxacyclopentane [tetrahydrofuran, (CH2)40] ... 

This process was first illustrated by Binger and Roster in 1974 (Scheme 17).35 Taking advantage of the readily available alkynyl-borates 21 (obtained by addition of alkynyl lithium or sodium compounds to triorganylboranes),36 the PBs 22a-d were prepared in good to excellent yields. During their investigation of the stereoselectivity of this... 

Addition of aryl lithium compounds to a (l-alkynyl)carbene complex la,b affords Michael adducts 90 in up to 45% yield, together with cyclopen-... 

Organocerium reagents are prepared in situ by the reaction of organolithium compounds with anhydrous cerium chloride or ceriiun iodide, as shown in equation (1). A variety of organolithium compounds can be employed, including alkyl-, allyl-, alkenyl- and alkynyl-lithiums, which are all converted to the corresponding cerium reagents. 

A large variety of cuprates are known nowadays. They include heteroleptic derivatives R(Y)CuM (Y = alkynyl, halide, amido, alkoxide, thiolato, phosphide M = Li or Mg), and have found widespread application in organic chemistry. Their syntheses and applications are discussed in the other chapters of this book. In addition, compounds in which the copper to lithium (or magnesium) ratio differs from 1 1 are also known examples are R3CuLi2 and the so-called higher order cyanocuprates introduced by Lipshutz et al. [99]. 

The hypervalent tin compound 350 reacts with the strong base lithium diethylamide leading to the elimination of chloride and subsequent coordination between B-N-Sn to form azoniastannaboratole derivative 351 (Equation 18) <2003JOM188>. The starting materials (m-borylstannanes 350) can be obtained by the organoboration of alkynyl-stannanes stereoselectively. 

Depending on the nature of the R groups of the alkynyl selenides 99, vinylic species with different regio- and stereochemistry are obtained (Scheme 62). When R is an alkyl group, mixture of products of different regiochemistry is obtained,179 which makes this method unsuitable for the preparation of this class of compounds. A solution for this problem consists in the use of lithium alkynyl selenolates 102 as precursors of the vinylzirconium species 103, as shown in Scheme 63.1... 

The trans allylic alcohol needed to make this compound was made using one of the methods we introduced in Chapter 3i reduction of an alkynyl alcohol with LiAlEL]. Here is the full synthesis alkylation of an ester enolate with prenyl bromide gives a new ester, which itself is turned into an alkylating agent by reduction and tosylation. The alkyne is introduced as its lithium derivative with the alcohol protected as a THP acetal. Hydrolysis of the acetal with aqueous acid gives the hydroxy-alkyne needed for reduction to the E double bond, which is then epoxidized. 

Metalatlon of 2-alkynyl and 1,2-alkadienyl tetrahydropyranyl ethers furane synthesis. /-Butyllithium metalates the lithium alkoxide 1 to afford the allenyllithium compound a quantitatively. This anion reacts with alkyl halides or CH3OH to afford 2. Another metalation-alkylation protonation sequence proceeds via b to afford 3. Hydrolysis of the latter intermediate affords furanes directly. The overall sequence can be performed in one pot from a propargyl tetrahydropyranyl ether, r-butyl-lithium, and an aldehyde. ... 

Besides processes (1) and (2), the reader should be aware that nucleophilic attacks on alkynes are treated in other chapters of this book, dealing with rearrangements, cyclizations, polyacetylenes, cyclic acetylenes and perhaps others. A number of publications overlap with ours in different ways and at different levels -. They treat individual alkynes or families " , e.g. acetylene, diacetylenes , acetylene dicarboxylic esters haloacetylenes , alkynyl ethers and thioethers > ynamines , fluoro-alkynes ethynyl ketpnes , nitroalkynes , etc. synthetic targets, e.g. pyrazoles , if-l,2,3-triazoles , isothiazoles , indolizines S etc. reagents, e.g. nitrones , lithium aluminium hydride , heterocyclic A -oxides - , azomethine ylids - , tertiary phosphorus compounds , miscellaneous dipolar nucleophiles - , etc. The reader will appreciate that all of these constitute alternate entries into our subject. 

---