Benito Alcaide

The controlled preparation of two types of α-seleno-α,β-unsaturated carbonyls, namely, α-selenoenals and α-selenoenones, have been accomplished.

Several heterocycles reacted with shelf-stable 2-(2-fluoropyridinium-1-yl)-1,1-bis[(trifluoromethyl)sulfonyl] ethan-1-ide, a latent Tf₂CCH₂ source, to give rise in a mild and controllable way to adducts via direct C–H bis[(trifluoromethyl)sulfonyl]ethylation reactions. This metal- and irradiation-free protocol is convenient. Besides, the volatile side-product 2-fluoropyridine can be smoothly eliminated under vacuum, which facilitates purification. The substrate scope survey discloses that exquisite chemo- and regioselectivities are achieved in a variety of heterocyclic systems. Of particular interest are the late-stage structural modification of known pharmaceuticals, such as the marketed drugs Phenazone (Antipyrine) and Edaravone, and the development of a water soluble fluorescent dye.

Phosphorus 1,3‐ and 1,4‐carbabetaines with ′P(+)−C−C(−)′ and ′P(+)−C−C−C(−)′ structures, respectively, in which the carbanion moiety was significantly stabilized by two trifluoromethylsulfonyl groups, have been synthesized and characterized. Analysis of their X‐ray crystal structures revealed that any attractive interactions between the anionic and cationic moieties were negligibly weak. This result was corroborated by using natural bond orbital (NBO) and Bader′s quantum theory of atoms in molecules (QTAIM) models. In contrast, performing the same analysis of a known 1,3‐carbabetaine equivalent, which can be drawn as a ′P(+)−C−C=C−O(−)′ resonance structure, revealed pronounced charge‐transfer interactions between the anionic and cationic moieties.

Functionalized ynones can be activated by Tf₂C=CH₂, which was generated in situ, to form zwitterionic species. These species were trapped in an intramolecular fashion by several nucleophiles to generate two major types of triflones in a divergent manner. Through fine‐tuning of the reaction temperature, bis(triflyl)‐6‐membered‐ or (triflyl)‐5‐membered‐fused‐heterocycles were achieved in reasonable yields in a totally selective manner. In this way, bis(triflyl)flavones, bis(triflyl)thioflavones, bis(triflyl)selenoflavones, (triflyl)benzothienopyrans, (triflyl)benzoselenophenopyrans, (triflyl)vinyl aurones, and (triflyl)pyranoindoles were constructed. Conceivable mechanistic pathways were suggested on the basis of the isolation of several intermediates and the results from control experiments.

New azahelicenes having interesting photophysical properties have been prepared in a four‐step sequence. These [7]helicenocarbazoles are efficient blue luminophores, demonstrating the utility of gold catalysis in the preparation of advanced materials.

Indole‐tethered amino allenynes were chemodivergently cyclized for the controlled preparation of fused polycyclic indoles using gold catalysis. Double cyclization of terminal allenynes afforded hexacyclic 15 H‐indolo[1,2,3‐de]quinolino[3,2,1‐ij]quinoxalines, in which allenynes bearing a substituted alkyne at the terminal end generated 12,13‐dihydro‐7 H‐indolo[3,2‐c]acridines, which are 5‐membered cyclized adducts. Density functional theory calculations were performed to shed light on this difference in reactivity.

The divergent and selective syntheses of two types of annelated β-lactams, namely, furan- and tetrahydropyridine-fused 2-azetidinones, have been accomplished directly from 2-azetidinone-tethered oxazolidine-enynes through gold catalysis.

An unprecedented metal‐free direct preparation of unprotected α‐hydroxy ketones from terminal alkynes under mild conditions with diazonium salts as the arene source and without the requirement of irradiation is described. The process is general and fully compatible with a wide variety of substitution in both reactants. Experimental and computational evidence strongly suggest the involvement of radical species in the transformation.

2‐Pyrrolines and 6‐oxo‐hexa‐2,4‐dienals have been prepared through the divergent reactions of 1‐benzenesulfonyl‐4‐aryl‐1,2,3‐triazoles with functionalized allenes. The rhodium‐catalyzed reactions between allenols and 1‐benzenesulfonyl‐4‐aryl‐1,2,3‐triazoles yielded 2‐pyrrolines. This transformation is compatible with the presence of aliphatic, aromatic, heterocyclic, amide, and halogen functional groups. Interestingly, a reactivity switch took place when the allene‐tethered alcohol substrate was replaced by its ketone counterpart. When the rhodium‐catalyzed reaction of 1‐benzenesulfonyl‐4‐phenyl‐1,2,3‐triazole was performed with allenones, acyclic 6‐oxo‐hexa‐2,4‐dienals were stereoselectively formed as (2Z,4E) isomers.

The room temperature radical cycloetherification/arylation cascade of allenols and diazonium salts has been accomplished via a combination of gold and photoredox catalysis to provide 2,3,4‐trisubstituted‐2,5‐dihydrofurans. The functionalized oxacycle formation sequence is chemo‐ and regioselective for the cycloetherification and for the position that bears the aryl moiety after the cross‐coupling. Mechanistic investigations revealed that this transformation proceeds through an initial oxidation of gold(I) to a phenyl gold(III) complex, which, upon coordination to the allene, catalyzes its cyclization and leads to the coupling product after a reductive elimination regenerating Au(I). magnified image