Metal-catalyzed cycloisomerization reactions of 1,n-enynes have appeared as conceptually and chemically highly attractive processes as they contribute to the highly demanded search for atom economy and allow the discovery of new reactions. Since the pioneering studies with palladium by the research group of Barry Trost in the mid-1980s, several other metals have been identified as excellent catalysts for the rearrangement of enyne skeletons. Moreover, the behavior of 1,n-enynes may be influenced by other functional groups such as alcohols, aldehydes, ethers, alkenes, or alkynes, thus enhancing the molecular complexity of the synthesized products. Apart from the intrinsic rearrangements of 1,n-enynes, several tandem reactions incorporating intramolecular trapping agents or intermolecular partners have been discovered. This Review aims to highlight the main contributions in this field of catalysis and to propose and comment on the mechanistic insights of the recent discoveries.

We report herein the synthesis and spectroscopic study of the first spiropyrandinolines that function as sensors for metal ions in the parts per billion range. These systems operate by either photochemically or chemically induced reversible formation of merocyanine metal ion complexes. The application of this novel photodynamic sensing material to sensor technology is discussed.

A highly efficient gold-catalyzed cycloisomerization reaction of bis-homopropargylic diols is described. The cyclizations are conducted in the presence of either AuI or AuIII catalysts in MeOH at room temperature in a very short time. The reaction conditions are compatible with functional groups, such as n-butyl, phenyl, allyl, benzyl, and alcohol groups, leading to original strained dioxabicyclo[2.2.1], -[2.2.2], or -[3.2.1] ketals in good to excellent yields.

A highly efficient gold-catalyzed cyclization reaction of various functionalized acetylenic acids is described. The cyclizations are conducted in the presence of Au(I) catalyst in acetonitrile at room temperature in a short reaction time. The reaction conditions are compatible with several functional groups, such as ester, alkene, alkyne, chloro, and free or protected alcohol, and lead to original gamma-lactones in good to excellent yields.

The palladium(0)-catalyzed diastereoselective dearomative cyclopentannulation of 3-nitroindoles with vinylcyclopropanes is described. This straightforward and highly atom-economical method leads to a wide range of functionalized indolines in good yields and diastereoselectivities and represents an unprecedented entry toward the valuable 2,3-fused cyclopentannulated indoline scaffold.

Different mechanisms have been proposed for the cyclization of enynes catalyzed by electrophilic metal halides or complexes. We present evidence to indicate that the previously reported “carbohydroxypalladation” and the “hydroxycyclization catalyzed by PtII” are closely related reactions. Thus, palladium complexes formed in situ from PdCl2 and trisulfonated phosphane TPPTS or cyclic phosphite P(OCH2)3CEt as the ligands catalyze the methoxy- or hydroxycyclization of enynes with selectivities similar to those observed with PtII complexes. Deuteration studies indicate that activation of the alkyne by PdII promotes an anti-addition of the alkene

The synthesis and characterization of original NHC ligands based on an imidazo[1,5‐a]pyridin‐3‐ylidene (IPy) scaffold functionalized with a flanking barbituric heterocycle is described as well as their use as tunable ligands for efficient gold‐catalyzed C−N, C−O, and C−C bond formations. High activity, regio‐, chemo‐, and stereoselectivities are obtained for hydroelementation and domino processes, underlining the excellent performance (TONs and TOFs) of these IPy‐based ligands in gold catalysis. The gold‐catalyzed domino reactions of 1,6‐enynes give rise to functionalized heterocycles in excellent isolated yields under mild conditions. The efficiency of the NHC gold 5Me complex is remarkable and mostly arises from a combination of steric protection and stabilization of the cationic AuI active species by ligand 1Me.

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