Alkynyl Grignard reagents, coupling with

The Ni-catalyzed cross-coupling reaction of alkynyl Grignard reagents 60 with ( )- or (Z)-dichloroethene 61a,b has been applied to a simple procedure for the preparation of the protected fomi 62a,b of a highly unstable synthon, as hexa-3-ene-l,5-diyne [Eq. (23). Separation of the diastereomers 62a and 62b is facile since the former is an oil and the latter is a solid [35]. 

Coupling of terminal acetylenes [top of 1, 169, after the formulation]. Miller173 has described a procedure for the cuprous chloride-catalyzed coupling of an alkynyl Grignard reagent (1) with propargyl bromide to produce a skipped 1,4-diyne (2) and its isomerization under mild conditions to a conjugated 1,3-diyne (3). 

Alternatively, the reaction of cyclopropylethynylmagnesium bromide with cyclo-propanone hemiacetal gives l-(cyclopropylethynyl)cyclopropanol (equation 152)232. The reaction of cyclopropanone acetal with other alkynyl Grignard reagents serves as a general route to alkynylcyclopropanols. Similarly, alkynyllithium derivatives of vitamin D were coupled with cyclopropane carbonyl isoxazolidine to give the corresponding alkynyl-cyclopropyl ketones (equation 153). 

Compounds containing four alkynyl groups attached to a single atom (C, Si, Ge) have been obtained by the coupling of alkynyl Grignard reagents with the appropriate tetrahalide . ... 

Dialkynyltellurides are easily formed by the reaction of alkynyl Grignard reagents or alkynyl lithium reagents with tellurium tetrachloride. The reaction mixtures contain significant amounts of the butadiyne, a typical ligand coupling reaction product. 

While alkynyllithiums react with primary alkyl halides in the presence of diamines or HMPA to afford the coupled products [35], this reaction proceeds slowly in the absence of these additives, even at elevated temperature. Luh has described a Pd/PPh3 catalyst that facilitates the cross-coupling of alkynyllithiums and alkynyl Grignard reagents with primary alkyl bromides and iodides (e.g.,Eq.l5) [37]. 

In contrast to reactions involving C(sp )-electrophiles that are well established, cross-couplings of alkynyl Grignard reagents with C(sp )-electrophiles are far... 

The use of cobalt species to catalyze cross-coupling reactions of activated or unactivated alkyl halides with alkynyl Grignard reagents in order to form C(sp)-G(sp ) bonds is also of interest. Cobalt compleres promote the crossbenzyl chlorides and bromides react with 2-trimethylsilylethynyl- and 1-octyn-l-ylmagnesium halides to provide l-aryl-2-alkynes in the presence of a catalytic amount of a cobalt complex [100,101]. 

Scheme 5.38 Ni-catalyzed cross-coupling of alkynyl Grignard reagents with vinyl...

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