Silver Triflate Catalyzed Tandem Heterocyclization/Alkynylation of 1‐((2‐Tosylamino)aryl)but‐2‐yne‐1,4‐diols to 2‐Alkynyl Indoles

Abstract

Don't cross me! 2-Alkynyl indoles were prepared efficiently by the AgOTf-catalyzed tandem heterocyclization/alkynylation of 1-(2-tosylamino)aryl)but-2-yne-1,4-diols under mild conditions (see scheme). The attractiveness of this approach lies in the fact that both the indole ring and alkyne side chain of the N-heterocycle are sequentially formed from low cost, readily available, and ecologically benign starting materials. It also provides the first route to this synthetically valuable class of compounds that is not based on a cross-coupling strategy.

Indole Synthesis Using Silver Catalysis

“…Twoy ears later,C han et al developed as ilver-catalyzed tandem heterocyclization/alkynylation process using propargylic 1,4-diols 33 to generate o-alkynyl indoles 34,l iberating two molecules of water as the sole by-products (Scheme 10). [15] This was the first reported indole synthesis that introduced alkyne moietiesa tt he 2-position of the indole ring withoutr elying on traditional cross-coupling methods. Av ariety of tosylprotected o-alkynyl indoles 34,b earing additional substituents in the 3-, 5-and 6-positions, wereg eneratedi ng ood to excellent yields employing AgOTf as the catalyst.I nterestingly,t he reactionp roceeds well in the absence of ag roup in the R 1 position, which leads to the formation of 3H-indole products;t his is particularly noteworthy as these products cannotb ef ormed using traditional cross-couplinga pproaches.…”

Tandem aldehyde–alkyne–amine coupling/cycloisomerization: A new synthesis of coumarins

“…This three-component coupling has been accomplished with a very broad range of transition metals, including copper, silver, gold, ruthenium/copper, cobalt, iridium and iron. Similarly, cycloisomerization of alkynols and alkynamines has also been an attractive approach for the synthesis of various known and new heterocyclic frameworks [2–22]. Various alkynophilic catalysts such as transition-metal catalysts (based on gold, mercury, platinum, silver, etc.…”

Rhodium(III)‐Catalyzed Cross Coupling of Sulfoxonium Ylides and 1,3‐Diynes to Produce Naphthol‐Indole Derivatives: An Arene ortho C−H Activation/Annulation Cascade

“…First, 1,3-diyne 2 a undergoes intramolecular hydroamination to generate 2-alkynyl indole intermediate 4 in the presence of AgSbF 6 . [10] Meanwhile, the cationic Cp*Rh III complex is generated upon treatment of [Cp*RhCl 2 ] 2 with AgSbF 6 , which then coordinates with sulfoxonium ylide 1 a and subsequently undergoes an ortho arene CÀ H activation to generate rhodacyclic intermediate A. The coordination of rhodium complex A with 4 gives intermediate B, which goes through a migratory insertion to afford intermediate C. Then, another Rh III intermediate D can be formed through an intramolecular rearrangement, which in turn gives the reactive carbenoid species E by α-elimination of DMSO with the assistance of Zn(OAc) 2 .…”