Cross-coupling 1-haloalkynes

The chemistry of haloalkynes with low-valent metal complexes has been reviewed.142 Two competing reactions of anionic metal carbonyls [M(CO) ] with halo-alkynes are (i) abstraction of X+ to give MX(CO) and (ii) nucleophilic displacement of X- to give M(C=CX)(CO) and M(CO) 2(ji-C=C). A recent study of reactions of haloalkynes with [M(CO)3Cp ]- (M = Cr, Mo, W Cp = Cp, Cp )] has clarified the reaction conditions, which are determined by the nucleophilicity of the anionic metal carbonyl and the electron-withdrawing power of any substituent on the C=C triple bond. Cross-coupling of the anion with a chloroalkyne is catalyzed by palladium.143... 

Cross-coupling of Haloalkynes with Organometallic Compounds... 

Cross-coupling of haloalkynes with organometallic compounds. 222... 

Using ( )-methylalkenylalanes 140, obtained by highly stereo- and regioselective Zr-catalyzed carboalumination of alkynes, the stereochemically defined enynes 141 can also by synthesized by Pd-catalyzed cross-coupling reactions with 1-haloalkynes [Eq. (47)] [68]. 

Some of the most useful synthetic transformations of terminal alkynes involve intermolecular and intramolecular homo- and cross-coupling reactions between their. sp-carbon centers, leading to butadiyne or polyyne derivatives. The two most widely used and practical systems are (i) oxidative homocoupling reactions, i.e. Glaser and Eglington reactions and (ii) heterocoupling reactions, i.e. Chodkiewicz-Cadiot coupling of a terminal alkyne with a haloalkyne. 

Both palladium and rhodium are effective catalysts, but the rhodium reactions seem to be more subject to steric effects. The reaction proceeds via a catalytic cycle similar to cross coupling, except that the formation of the diorgano(palladium) is brought about by electrophilic attack by the arylpalladium halide, rather than a transmetallation reaction, hence the need for electron-rich systems. The equivalent alkynylation can also be carried out using haloalkynes. ... 

Scheme 4.25 Cross-coupling of zinc-copper reagents and 1-haloalkynes [117].

Oxidative Cross-Coupiing Reactions C(sp )-organozincs can also take part in palladium-catalyzed oxidative cross-coupling reactions. C(sp )-C(sp) couplings, not easy to achieve by more classical approaches involving haloalkynes, are readily performed. 

Table 9.13 Selection of cross-couplings between alkynylcopper reagents and haloalkynes.

Highly synthetically demanding (. -hisubstituted alkenes and their derivatives (useful advanced intermediates for archazolid A and B, (+)-discodermolide and (—)-callystatin A) are prepared from 1-haloalkyne via hydroboration-migratory insertion-Zn-promoted iodinolysis-Pd-catalyzed organozinc cross-coupling (eq 27). ... 

Synthesis of Polyynes. Conjugated diyne and polyyne units, which exhibit unusual electrochemical, optical, and structural properties, can be efficiently constructed from 1-haloalkynes via homologation by one acetylene unit with TIPS-acetylene through a transition metal-catalyzed cross-coupling reaction, 2 which allows an access to a new class of polyyne framework. 

Scheme 7.85 Cross-coupling of zinc-copper organometallics with 1-haloalkynes.

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