Difunctionalization of alkynes

A tanden anh-vicinal difunctionalization of alkynes, involving the addition of a lithium organotellurolate to an activated alkyne, with subsequent trapping of the vinyllithium intermediate with electrophiles, was recently reported and named electrotelluration. ... 

Ruthenium-catalyzed 1,1-difunctionalization of alkynes can be achieved through ruthenium vinylidene intermediates. In this context, Lee s group reported the... 

Besset T, Poisson T, Pannecoucke X (2015) Direct vicinal difunctionalization of alkynes an efficient approach towards the synthesis of highly functionalized fluorinated alkenes. Eur J Org Chem 13 2765-2789... 

A similar but conceptually distinct approach to difunctionalization of terminal alkynes consists of sequential carboboration-palladium-catalyzed cross-coupling 137 equation (33) illustrates that this method also provides alkenes of high stereochemical purity by net syn Markovnikov addition. Benzyne-contain-ing molecules can act as highly activated substrates for vicinal difunctionalizations initiated by nucleophiles 138-140 thus, nucleophilic addition-electrophilic trapping can serve as an alternative to sequential directed metallation for the production of 1,2-disubstituted and 1,2,3-trisubstituted aromatic systems (equation 34).141... 

Fig. 19 Iron(II)-catalyzed intramolecular vicinal difunctionalization of alkenes or alkynes...

Z)-2-Bromoalkenyl boronates. These compounds are obtained by treatment of alkynes with BBr and subsequent quenching with an alcohol. As both the bromine atom and the boron residue can be selectively replaced, the difunctionalized alkenes are useful synthetic intermediates. 

Silastannylation of alkynes. The partitional difunctionalization is achieved using a catalytic system of Pd(OAc)j-RNC at room temperature (75-99% yield). The many chemoselective coupling procedures available to vinyltin and silicon compounds make these product extremely valuable for synthetic quests. 

Alkynes can be transformed into alkenylstannanes by reaction with stannyl-cuprates. It is possible to trap the 1,2-dimetallic alkene species with various electrophiles. The analogous vicinal difunctionalization of alkynyl selenides " has also been reported. A route to trisubstituted alkenes from phenylthioacetylene"" starts with cuprate addition, but a 1,2-metal rearrangment is involved. Enamines are obtained from N-ethynyldiphenylamine. The alkenylcopper intermediate is also reactive toward many electrophiles. Silylcupration of functionalized alkynes may lead to cyclic products by virtue of intramolecular alkylation. ... 

Alternatively, hydride reduction of manganacycle 12 results in the incorporation of a second molecule of carbon mcmoxide and formation of butenolide 14. This unique transformation involves fcmnation of three carbon-carbon bonds, two molecules of CO being incorporated, and difunctionalization of an alkyne in a completely regioselective manner. 

In contrast, unactivated olefins and alkynes complexed to organopalladium species generated in situ by oxidative addition of an unsaturated halide to a palladium(0) complex react intramolecularly with stabilized nucleophiles. These reactions that require catalytic quantities of the metal result in overall difunctionalization of the olefinic or acetylenic substrates. 

When alkynic esters are used as substrates in the reaction sequence, activated alkenes of good isomeric purity can be prepared. Initiation of the difunctionalization usually is by means of organocopper-medi-ated 1,4-addition, which proceeds via carbometallation of the alkynyl moiety of the ester to give a vi-nylcopper intermediate, (14). Trapping by an electrophile affords cis-difunctionalized alkenoates... 

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