Silver(I)-catalyzed tandem 1,3-acyloxy migration/Mannich-type addition/elimination of the sulfonyl group of N-sulfonylhydrazone-propargylic esters to 5,6-dihydropyridazin-4-one derivatives

Rhodium(i)-catalysed cycloisomerisation/6π electrocyclisation of 5-(ethynylamino)pent-2-yn-1-yl esters to 2,3-dihydrobenzo[f]indoles

A rare instance in rhodium catalysis of an in situ formed rhodacycle that undergoes a formal 1,8-acyloxy migration-initiated reductive elimination.

Pyrazole synthesis via a cascade Sonogashira coupling/cyclization of N-propargyl sulfonylhydrazones

An efficient approach for the preparation of pyrazoles via a Pd(ii)/Cu(i)-catalyzed Sonogashira coupling/cyclization of N-propargyl sulfonylhydrazones has been established.

Brønsted Acid-Mediated Cycloaromatization of 1H-Indol-2-yl Propargyl Benzoates to 7H-Benzo[c]carbazoles

A synthetic method for the efficient assembly of benzo[c]carbazole derivatives that relies on silica gel-activated benzoic acid-mediated cycloaromatization of 1H-indol-2-yl propargyl benzoates under atmospheric conditions is described. Robust with a variety of substitution patterns tolerated, the reaction provides a one-step strategy to construct a member of the N-heterocycles family in good to excellent yields. A tentative mechanism is proposed in which the cycloaromatization process is thought to involve a Brønsted acid-mediated formal 1,3-acyloxy migration/6π-electrocyclization pathway.

Silver(I)-Catalyzed Intramolecular Cyclizations of Epoxide-Propargylic Esters to 1,4-Oxazine Derivatives

An interesting silver(I)‐catalyzed, one‐pot intramolecular cyclization of epoxide‐propargylic esters is described. A variety of 1,4‐oxazine derivatives were obtained through a novel domino sequence, including three‐membered ring‐opening, 3,3‐sigmatropic rearrangement, 6‐exo‐cycloisomerization and subsequent intramolecular elimination in moderate yields under mild conditions.

Synthesis of pyrazolo[5,1-a]isoquinolines through copper-catalyzed regioselective bicyclization of N-propargylic sulfonylhydrazones

An expeditious strategy for the synthesis of pyrazolo[5,1-a]isoquinolines through copper(ii)-catalyzed regioselective bicyclization of N-propargylic sulfonylhydrazones has been developed.

Triflic Acid-Catalyzed Enynes Cyclization: A New Strategy beyond Electrophilic π-Activation

The cyclization of enynes, catalyzed by a transition metal, represents a powerful tool to construct an array of cyclic compounds through electrophilic π-activation. In this paper, we disclose a new and efficient strategy for enynes cyclization catalyzed by triflic acid. The salient features of this transformation includes a broad substrate scope, metal free synthesis, open flask and mild conditions, good yields, ease of operation, low catalyst loading, and easy scale-up to gram scale. A preliminary mechanism study demonstrated that the activation model of the reaction was σ-activation, which is different from the transition-metal-catalyzed enynes cyclization. Our strategy affords a complementary method to the traditional strategies, which use transition-metal catalysts.

Gold(i)-catalyzed highly stereoselective synthesis of polycyclic indolines: the construction of four contiguous stereocenters

A convenient and efficient synthetic method has been developed to construct highly functionalized polycyclic indoline skeletons with four contiguous stereocenters.

Gold(i) catalyzed tandem cyclization of propargylic esters to 4-acyloxy-1,2-dihydroquinolines

Gold catalyzed tandem [3,3]-rearrangement and intramolecular hydroamination of propargylic esters has been disclosed in this communication, producing a series of 4-acyloxy-1,2-dihydroquinolines in good yields and high enantioselectivities.

Gold-Catalyzed Intramolecular Cyclizations of Cyclopropenes with Propargylic Esters

Homogeneous gold catalysts are interesting as they can act as potent carbophilic Lewis acids to activate the π bonds of alkynes, allenes, and alkenes. Many impressive applications for the formation of C−C or C−heteroatom bonds have been found due to the excellent functional group compatibility of these catalysts and the air and moisture tolerance of their reactions. Here, we have developed gold‐catalyzed novel intramolecular cycloisomerizations of nitrogen or oxygen‐tethered cyclopropenes with propargylic esters. The reaction proceeded through different pathways according to different substituent styles, affording 5‐azaspiro[2.5]oct‐7‐enes and bicyclo[4.1.0]heptanes.

Silver-catalysed reactions of alkynes: recent advances

Silver is a less expensive noble metal. Superior alkynophilicity due to π-coordination with the carbon-carbon triple bond makes silver salts ideal catalysts for alkyne-based organic reactions. This review highlights the progress in alkyne chemistry via silver catalysis primarily over the past five years (ca. 2010-2014). The discussion is developed in terms of the bond type formed with the acetylenic carbon (i.e., C-C, C-N, C-O, C-Halo, C-P and C-B). Compared with other coinage metals such as Au and Cu, silver catalysis is frequently observed to be unique. This critical review clearly indicates that silver catalysis provides a significant impetus to the rapid evolution of alkyne-based organic reactions, such as alkynylation, hydrofunctionalization, cycloaddition, cycloisomerization, and cascade reactions.