Alkenyllithium compounds

The organoborate intermediates can also be generated from alkenylboronic esters and alkyllithium or Grignard reagents, or from ttialkylboranes and alkenyllithium compounds. Conjugated symmetrical and unsymmetrical diynes (289—291), stereochemically pure 1,3-dienes (292,293), and 1,3-enynes (294) including functionali2ed systems can be prepared (289,295). 

Hetero-substituted 2-alkenyllithium compounds, however, show useful levels of regio- and stereoselectivity in reactions with aldehydes, in particular if the cation is held at one terminus of the allylie system by electron-withdrawing or chelating groups. 

Alkenyllithium compounds are intermediates in the Shapiro reaction, which is discussed in Section 5.7.2. The reaction can be run in such a way that the organolithium compound is generated in high yield and subsequently allowed to react with a variety of electrophiles.64 This method provides a route to vinyllithium compounds starting from a ketone. 

Alkenyl fluorides.1 Alkenyllithium compounds, obtained from reaction of alkenyl iodides with J-butyllithium, are converted into alkenyl fluorides by reaction with an N-f-butyl-N-fluorobenzenesulfonamide (1) in THF/ether/pentane at -120 - 20° yields 71-88%. 

To the best of our knowledge, X-ray structural data of complexes with simple dihapto interactions between a lithium atom and the n system of an alkene or alkyne ligand are unknown, but there is some spectroscopic evidence for weak it interactions in solutions of 3-alkenyllithium compounds from 7Li-and H-NMR data (4). Interactions of this sort are presumably important in addition (polymerization) reactions between organolithium compounds and alkenes or alkynes. 

Fig. 13.11. Stereoselective preparations of cw-alkenylboronic acids and the corresponding diisopropyl ester starting with cw-bromoalkenes. The first step involves a Br/Li exchange to form the alkenyllithium compound B. This organolithium compound is subsequently transmetallated to give complex C by using B(0 Pr)3.

Alkenyllithium compounds can also be prepared by metaUation of alkenes, particularly when alkenyl hydrogens are rendered acidic by an a-substituent (equation 22). Transmetallation of alkenyl stannanes with organohthium reagents gives alkenyUithium compounds with retention of alkene stereochemistry (equation 23). Tin lithium fransmet-allation has been used to prepare 1,4-dihthio-l,3-butadiene. Monosubstituted alkenylhthium compounds RHC=CHLi, can also be prepared from the corresponding diorganotel-luride, RHC=CHTeBu, by reaction with butylhthium in... 

Vinyllithium is tetrameric in THF solution. Alkenyllithium compounds containing a-hydrogen or-aUcyl substituents do not isomerize readily however, the presence of donor solvents promotes (Z)-to-( ) isomerization. Those compounds containing a-aryl substituents isomerize readily. The configurational stabilities of HDC=C(Li)X, where X is CN or C02Me, and RHC=C(Li)Y, where Y is OR or MesSi, have been investigated. 

This configurationaly stable organozinc halide is in sharp contrast with the alkenyllithium compounds bearing silyl substituents described in Ref. [15]. 

The aryl- or alkenyllithium compounds that are obtained from halogen-metal exchange are used as nucleophiles in subsequent reactions, usually toward 7t-bond electrophiles such as carbonyl compounds. 

The rearrangement of such alkenyllithium compounds is also used for synthetic purposes 107). 

Chiral, Non-Racemic l-Oxy-2-Alkenyllithium Compounds by Sparteine-Mediated Deprotonation and Stereochemical... 

This methodology has been employed in the total synthesis of trisphaeridine and N-methylcrinasiadine, providing a concise synthetic route to these phenanth-ridine alkaloids [56]. The intramolecular anionic benzyne cychzation has also been successfully extended to benzyne-tethered alkenyllithium compounds, but the methodology is limited to the preparation of indole derivatives. Extensions of this... 

They are easily prepared by treatment of an alkyl, aryl, or alkenyllithium compound with copper(l) iodide, as illustrated by the preparation of lithium dibutyl-copper from butyllithium. 

Homillos V, Giannerini M, Vila C, Fananas-Mastral M, Feringa BL (2015) Direct catalytic cross-coupling of alkenyllithium compounds. Chem Sci 6 1394—1398... 

The C-disaccharide 43 (2-deaminotunicmnycin) and its 7-epimer have been synthesized by addition of the 6-deoxy-6-diazo-D-galactose derivative 40 to aldehyde 29, followed by LiBHEta-reduction of the ketone 41 and epoxide 42 thus obtained as a separable mixture (Scheme 6). The preparation of the first pseudo-C-disacchande by use of the alkenyllithium compound derived from dibromoalkene 44 is covered in Chapter 18. 

Xi Z, Song Q, Chen J, Guan H, Li P (2001) Dialkenylation of carbonyl groups by alkenyllithium compounds formation of cyclopentadiene derivatives by the reaction of... 

Dianions 126, alkenyllithium compounds of type VIII, have been obtained by halogen-lithium exchange from the corresponding chlorinated or brominated precursors 125 using lithium naphthalenide it was necessary to carry out a previous deprotonation with PhLi. The reaction of 126 with electrophiles gave regio-selective functionalized allyl amines 127 (Scheme 2.17) [106]. 

As an example of a remote functionalized alkenyllithium compound, the alkoxy functionalized polyenyllithium 236 (prepared from 235 by bromine-lithium exchange with t-BuLi) reacted with carbonyl compounds to give after acidic hydrolysis the corresponding polyenic aldehydes 237 (Scheme 2.32) [193]. 

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