Lithium vinylcuprates

Lithium vinylcuprates.2 Treatment of trisylhydrazones with 2 equivalents of t-butyllithium to generate the vinyllilhium reagent (9, 486 -487) followed by addition... 

One of the steps in a route leading to prostaglandin synthesis is a reaction of lithium vinylcuprate (Eq. 269). ... 

Naf, F., and P. Degen Stereospecific Olefin Synthesis via Lithium Vinylcuprates. Helv. Chim. Acta 54, 1939 (1971). 

Scheme 3.18. Ring-formation by intramolecular trapping of the vinylcuprates resulting from silylcupration of alkynes with magnesium silylcuprates [75a] or lithium silylcuprates (mCPBA = m-chloroperbenzoic acid) [75bj.

Various functionalized alkynes can be submitted to carbocupration reactions, such as alkoxyalkynes,150 alkynyl carbamates,151 acetylenic orthoesters,152 and thioalkynes.153 The carbocupration of orthoesters, for example, 204, has been used to prepare a-substituted esters of the type 206 by acidic hydrolysis of the adduct 205 (Scheme 51).152 This allows the formation of regioisomers that are not accessible by copper-mediated addition to acetylenic esters. A stereoselective synthesis of trisubstituted alkenes has been described by Normant et al.lSd> starting from phenylthio-acetylene 207. Carbocupration with lithium di- -butylcuprate affords the intermediate 208 which, upon addition of /z-butyllithium, undergoes a 1,2-metalate rearrangement to the vinylcuprate 209. The latter can be trapped with various electrophiles, for example, ethyl propiolate, providing product 210 with complete regio- and stereocontrol. 

The reaction of various electrophiles with vinylcuprates, formed by addition of lithium n-butylcyanocuprate to acetylenic selenides afforded, a-substituted vinylic selenides in reasonable to good yields (50-76%) [661 (Scheme 53, reaction 1). Starting from phenylselanylacetylene, the two groups introduced have a cis configuration [67,681. A loss of stereoselectivity was observed after hydroly-... 

Lithium a-carbomelhoxy (1 -hexynyl)-vinylcuprate, 330 Lithium carbonate, 17, 18 Lithium chloroacetylide, 293... 

Cuprate species of the type R3Cu2MgX (X = Cl or Br) add regio- (and stereo-) specifically to terminal acetylenes to give 1,1-disubstituted olefins e.g. (46) - (47). ° The choice of starting materials from which the cuprates are generated, as well as the incorporation of an excess of lithium bromide, is important if dimerization of the intermediate vinylcuprates is to be avoided. 

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