Oxy- and Chloroarylation Pathways in Gold-Mediated Cyclization of 2-Aminoaryl-3-arylpropargyl-benzenesulfonamides.

A one-pot diazotization/gold-mediated cyclization of 2-aminoaryl-3-arylpropargyl-benzenesulfonamides is described. After diazotization, Me2 SAuCl triggers an oxy- and/or chloroarylation of the alkyne moiety, resulting in the formation of 3-acylindoles and/or Z-3-(chloromethylene)indolines. Density Functional Theory (DFT) calculations show the significant energetic preference of both processes over an insertion pathway. Notably, a Z-3-(chloromethylene)indoline crystallized with [Cl-Au-Cl],- exhibiting Au⋅⋅⋅H-C short contacts.

The Chameleonic Nature of the Nitro Group Applied to a Base-Promoted Cascade Reaction To Afford Indane-Fused Dihydrofurans.

We disclose a Michael/Conia-ene/SN2 cascade reaction for the synthesis of Indane-fused dihydrofurans from 1,3-dicarbonyl compounds and 2-alkynylnitrostyrenes promoted by potassium carbonate in DMSO at room temperature. In this reaction, the nitro group has a chameleonic role, first as an electron-withdrawing group for the Michael addition, then the nitronate behaves as a nucleophile, and finally, the allylic nitro acts as a leaving group. The product is obtained as a single diastereomer, affording up to 82% with 1,3-keto esters and 58% with 1,3-diketones. Furthermore, DFT calculations of the reaction mechanism explained the chemoselective addition of the nitronate over the enolate to the unactivated triple bond, with the enolate addition being highly endothermic.

SO2 capture and detection using a Cu(II)-metal-organic polyhedron.

The SO2 adsorption-desorption capacity at room temperature and 1 bar of the metal-organic polyhedron MOP-CDC was investigated. In addition, the qualitative solid-state absorption-emission properties of this material (before and after SO2 exposure) were measured and tested, and it demonstrated remarkable capability for SO2 detection. Our results represent the first example of fluorimetric SO2 detection in a MOP.

The effect of chiral N-substituents with methyl or trifluoromethyl groups on the catalytic performance of mono- and bifunctional thioureas.

We evaluated thiourea organocatalysts that incorporate a chiral group which includes a trifluoromethyl moiety and contrasted their performance with non-fluorinated analogs. The comparison between such systems allows the direct study of the NH acidity of a thiourea bonded to an aliphatic substituent. In principle, -CF3 systems feature an enhanced hydrogen bond (HB) donor capacity that is undoubtedly beneficial for HB-catalysis applied to the Baylis-Hillman reaction. We found that the thiourea substituted on both nitrogens with this group accelerates this reaction like Schreiner's thiourea. On the other hand, we observed a different behavior in reactions promoted by bifunctional catalysts (thiourea-primary amine). In the Michael addition of isobutyraldehyde to methyl benzylidenepyruvate, the -CF3 containing catalysts were better than the -CH3 systems, whereas the conjugate addition to N-phenylmaleimide showed the opposite behavior. Theoretical calculations of the transition states indicated that the phenylethyl group in fluorinated and non-fluorinated compounds have different kinds of interactions with the electrophile. These interactions are responsible for a different arrangement of the electrophile and thereby the selectivity of the catalyst. Therefore, it cannot be generalized that in all cases NH acidity correlates with the performance of the catalyst, particularly, with aliphatic substituents that unlike the aromatic ones possess groups that are outside the plane of the thiourea.

Stereocontrolled Nucleophilic Addition to Five-Membered Oxocarbenium Ions Directed by the Protecting Groups. Application to the Total Synthesis of (+)-Varitriol and of Two Diastereoisomers Thereof.

A stereodivergent C-glycosidation of carbohydrate-derived lactones can be mediated by the protecting groups and applied to the total synthesis of (+)-varitriol and of two diastereoisomers thereof, which represent an unprecedent use of the protecting groups in the synthesis of a naturally occurring compound. In particular, the stereoselective nucleophile attack for 2,3-trans-substituted five-membered ring oxocarbenium ions is strongly influenced by the presence of aromatic rings in the protecting groups. According to quantum chemical calculations, the stereoselectvity depends on the π-π interactions between the aromatic ring of the C-2 protecting group with the exocyclic triple bond and the oxocarbenium ion. These interactions account for the stabilization of the conformer in which the C-2 and C-3 substituents adopt pseudoaxial orientations. When protecting groups do not contain an aromatic ring, the sterochemical outcome is dictated by stereoelectronic factors established by the Woerpel's model. Based on these findings, a concise total synthesis of the natural product (+)-varitriol and of two diastereoisomers was acomplished.