Herein, a dual-gold catalyzed cyclization of 3,4-diethynylthiophenes generating pentaleno[c]thiophenes through gold-vinylidenes and CÀH bond activation is disclosed. Various new heteroaromatic compounds-substrate classes unexplored to date-exhibiting three five-membered annulated ring systems could be synthesized in moderate to high yields. By comparison of the solid-state structures of the corresponding gold-acetylides, it could be demonstrated that the cyclization mode (5-endo versus 6-endo) is controlled by the electronic and not steric nature of the diyne backbone. Depending on different backbones, we calculated thermodynamic stabilities and full potential-energy surfaces giving insight into the crucial dual-activation cyclization step. In the case of the 3,4-thiophene backbone, in which the initial cyclization is rate and selectivity determining, two energetically distinct transition states could be localized explaining the observed 5-endo cyclization mode by classical transition-state theory. In the case of vinyl and 2,3-thiophene backbones, the theoretical analysis of the cyclization mode in the bifurcated cyclization area demonstrated that classical transition-state theory is no longer valid to explain the high experimentally observed selectivity. Herein, for the first time, the influence of the backbone and the aromatic stabilization effect of the 6-endo product in the crucial cyclization step could be visualized and quantified by calculating and comparing the full potential-energy surfaces.

The nucleophilic addition of protected and substituted hydrazine derivatives to isonitrile complexes of gold(I), platinum(II), palladium(II) and rhodium(III) provides the corresponding hydrazino amino acyclic carbene complexes. These are characterized by their spectroscopic data, four different X‐ray single crystal structure analyses and their catalytic activity in the gold(I)‐catalyzed cycloisomerization of N‐propargylcarboxamides to alkylideneoxazolines is investigated.magnified image

HMF-derived substrates were converted to highly substituted phenols by gold catalysis.

An atom-efficient route to pyrroles substituted in the β-position has been achieved in four high yielding steps by a combination of Pd, Ru, and Fe catalysis with only water and ethene as side-products. The reaction is general and gives pyrroles substituted in the β-position with linear and branched alkyl, benzyl, or aryl groups in overall good yields. The synthetic route includes a Pd-catalyzed monoallylation step of amines with substituted allylic alcohols that proceeds to yield the monoallylated products in moderate to excellent yields. In a second step, unsymmetrical diallylated aromatic amines are generated from the reaction of a second allylic alcohol with high selectivity in moderate to good yields by control of the reaction temperature. Ru-catalyzed ring-closing metathesis performed on the diallylated aromatic amines yields the pyrrolines substituted in the β-position in excellent yields. By addition of ferric chloride to the reaction mixture, a selective aromatization to yield the corresponding pyrroles substituted in the β-position was achieved. A reaction mechanism involving a palladium hydride, generated from insertion of palladium to O-H of an allyl alcohol, that is responsible for the C-O bond cleavage to generate the π-allyl intermediate is proposed.

Gold-Catalyzed Cyclization of Diynes: Controlling the Mode of 5-endo versus 6-endo Cyclization -An Experimental and Theoretical Study by UtilizingDiethynylthiophenes. -A dual-gold catalyzed cyclization of 3,4-diethynylthiophenes generating new heteroaromatic compounds bearing five-membered annulated ring systems is reported. By comparison of the solid-state structures of the corresponding gold-acetylides, it is demonstrated that the cyclization mode (5-endo vs. 6-endo) is controlled by the electronic and not steric nature of the diyne backbone. Extensive physicochemical studies are disclosed. For the first time, the influence of the backbone and the aromatic stabilization effect of the 6-endo product in the crucial cyclization step are visualized and quantified by calculating and comparing the full potential-energy surfaces. -(HANSMANN, M. M.; TSUPOVA, S.; RUDOLPH, M.; ROMINGER, F.; HASHMI*, A. S. K.; Chem. -Eur.

Palladium-catalyzed allylation of hydrazines using allyl alcohols is reported. This highly efficient protocol furnishes monoallylated hydrazines selectively, in 27-99% yields. Following an optimization of the reaction conditions and of the Pd-ligands, the allylations of both mono- and disubstituted hydrazines were investigated, as well as the effects of C2-substitution on the allylating agent. Of particular interest, a novel method for the selective monoallylation of monosubstituted hydrazines is demonstrated.

A new pathway in dual gold-catalyzed reaction of thiophene-tethered diynes has been identified. A series of fully conjugated alkynyl-substituted benzothiophenes and benzofurans was obtained by a formal cyclisation/dimerization sequence. All the products are fluorescent, owing to their extended conjugation. The mechanistic studies have been carried out, suggesting that gold acetylides take part in this transformation.

Novel dialkynyl pyridines were synthesized and protected as alkyl salts for dual gold(I)‐catalyzed cycloisomerization. Different alkyl groups and counter ions were screened for the salts, with benzyl and hexafluorophosphate providing the best results. The cyclization led to NMR yields of >95 % being obtained for a number of substrates. Step‐wise hydrogenation of products could be performed in one‐pot by Pd/C, with selective reduction of the double bonds, followed by deprotection of the benzyl group.