Pd-catalysed C-H functionalisation of free carboxylic acid has gained significant attention over the last few years due to the predominance of carboxylic acid moieties in pharmaceuticals and agrochemicals. But their...
The intra- and intermolecular Pd-catalysed cyanosulfenylation of internal alkynes enables the formation of tetrasubstituted thioacrylonitriles and is extended to oligoyne systems leading to oligoenes and a cyanide transfer over four or six atoms.
The intra-and intermolecular synthesis of selenium-substituted acyclic and heterocyclic acrylonitrile derivatives is presented. The 1,2-difunctionalization of several internal alkynes substituted not only by aliphatic and aromatic residues but also by heteroelements is realized by the Pd-catalyzed activation of aromatic and aliphatic selenocyanates. A high functional group tolerance allows straightforward access to a broad scope of tetrasubstituted olefins. X-ray studies of some products reveal noncovalent chalcogen−chalcogen interactions between oxygen and selenium.
A phosphine-catalyzed
oligomerization of arynes using selenocyanates
was developed. The use of JohnPhos as a bulky phosphine is the key
to accessing α,ω-bisfunctionalized oligo(ortho-arylenes) with RSe as the substituent at one terminus and CN as
the substituent at the other. The in situ formation
of R3PSeR′ cations, serving as sterically encumbered
electrophiles, hinders the immediate reaction that affords the 1,2-bisfunctionalization
product and instead opens a competitive pathway leading to oligomerization.
Various optimized conditions for the predominant formation of dimers,
but also for higher oligomers such as trimers and tetramers, were
developed. Depending on the electronic properties of the electrophilic
reaction partner, even compounds up to octamers were isolated. Optimization
experiments revealed that a properly tuned phosphine as catalyst is
of crucial importance. Mechanistic studies demonstrated that the cascade
starts with the attack of cyanide; aryne insertion into n-mers leading to (n+1)-mers was ruled out.
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