Catalytic Rearrangement of 2‑Alkoxy Diallyl Alcohols: Access to Polysubstituted Cyclopentenones

A catalytic rearrangement of diallyl alcohols comprising a cyclic enol ether has been developed using very mild conditions. Bismuth­(III) triflate was found to be a very active catalyst for the ring rearrangement of a range of tertiary allylic alcohols to efficiently afford polysubstituted cyclopentenones with a high degree of diastereoselectivity

Bi(OTf)₃-Catalyzed Cycloisomerization of Aryl-Allenes

Intramolecular hydroarylation of allenes was achieved under very mild conditions using bismuth(III) triflate as the catalyst. Efficient functionalization of activated and nonactivated aromatic nuclei led to C–C bond formation through a formal Ar–H activation. A tandem bis-hydroarylation of the allene moiety was also developed giving access to various interesting polycyclic structures

Bi(OTf)₃-Catalyzed Cycloisomerization of Aryl-Allenes

Intramolecular hydroarylation of allenes was achieved under very mild conditions using bismuth(III) triflate as the catalyst. Efficient functionalization of activated and nonactivated aromatic nuclei led to C–C bond formation through a formal Ar–H activation. A tandem bis-hydroarylation of the allene moiety was also developed giving access to various interesting polycyclic structures

Cycloisomerization of Allene–Enol Ethers under Bi(OTf)₃ Catalysis

The cycloisomerization of allene–enol ethers under Bi­(OTf)₃ catalysis was developed as a novel “atom-economic” tool for accessing interesting functionalized cyclopentene rings. Bi­(OTf)₃ was shown to promote selectively the activation of the enol ether moiety of the substrate. This catalytic methodology was further extended to the synthesis of dihydrofuran and oxaspirocycle derivatives

Synthesis of Stable Pentacoordinate Silicon(IV)–NHC Adducts: An Entry to Anionic N‑Heterocyclic Carbene Ligands

This work features the previously undescribed interactions of Martin’s spirosilane with different types of N-heterocyclic carbenes (NHCs). The level of interaction proved to be strongly dependent on the size of the Lewis base and could vary from the formation of isolable classical Lewis adducts to abnormal Lewis adducts, as evidenced by X-ray diffraction structure analyses and NMR studies. It has been found that abnormal adducts could be used as precursors for the synthesis of anionic NHCs bearing a weakly coordinating siliconate component. Complexation of these new types of carbenes with gold­(I) and copper­(I) has been efficiently accomplished. DFT calculations performed on the siliconate-based anionic NHC ligands revealed a high-lying HOMO and therefore a strong σ-donor character

Assessing Ligand and Counterion Effects in the Noble Metal Catalyzed Cycloisomerization Reactions of 1,6-Allenynes: a Combined Experimental and Theoretical Approach

1,6-Allenynes are useful mechanistic probes in noble-metal catalysis, since they can give rise to very distinct products in a highly selective fashion. Various cycloisomerization reactions have been described, and discrete mechanisms have been postulated. Of particular interest, whereas Alder-ene types of products can be obtained in a variety of ways using noble-metal catalysts (Au, Pt, Rh, ...), hydrindienes have been reported solely with gold and platinum under specific conditions. It was shown in a previous study that this intriguing transformation required the presence of chloride ligands at the active catalytic species. Herein, the factors governing the fate of 1,6-allenynes under cycloisomerization conditions have been studied more thoroughly, revealing a much more complex scenario. The nature of ligands, counterions, and metals was examined, showing that hydrindienes can be isolated in the absence of halides, using electron-rich, bulky triorganophosphines or carbene ligands. This crucial finding could also be used to access hydrindienes in high yields, not only with gold or platinum but also with silver. On the basis of mass spectrometry, NMR spectroscopy, and computations, refined mechanistic scenarios have been put forward, also rationalizing counterion effects. Notably, a metal vinylidene intermediate has been proposed for the formation of the hydrindiene derivatives. Finally, in the presence of tris­((triphenylphosphine)­gold)­oxonium tetrafluoroborate as catalyst, a new pathway has been unveiled, involving gold alkyne σ,π complexes and leading to previously unobserved [2 + 2] cycloaddition compounds