Benzannulation of Triynes Initiated by an Alder-Ene Reaction and Subsequent Trifluoromethylthiolate Addition

Intramolecular rhodium-catalysed [2 + 2 + 2] cycloaddition of linear chiral N-bridged triynes: straightforward access to fused tetrahydroisoquinoline core

A route for the preparation of merged symmetrical tetrahydroisoquinolines with central chirality through a rhodium-catalyzed intramolecular [2 + 2 + 2] cycloaddition involving enantiopure triynes as substrates is described. The results show that linear triynes lacking a 3-atom tether can undergo efficient cyclisation. The N-tethered 1,7,13-triynes used in our approach were easily prepared from readily accessible chiral homopropargyl amides, the basic building blocks in our approach, which were efficiently obtained by diastereoselective addition of propargyl magnesium bromide to Ellman imines. Additional substitution at the benzene rings could be attained when substituted triynes at the terminal triple bonds were employed, giving access to more complex tetrahydroisoquinolines after the rhodium-catalyzed intramolecular [2 + 2 + 2] cycloaddition. Among the different transition-metal catalysts, the Wilkinson complex (RhCl(PPh₃)₃) afforded higher yields in the cyclisation of linear triynes; however, triynes bearing a Br substituent at the terminal positions underwent the cyclisation more efficiently in the presence of [RhCl(CO)₂]₂.

Selectivity between an Alder–ene reaction and a [2 + 2] cycloaddition in the intramolecular reactions of allene-tethered arynes

Substituent-dependent reactivity and selectivity in the intramolecular reactions of arynes tethered with an allene are described.

Efficient synthesis of SCF3-substituted tryptanthrins by a radical tandem cyclization

Herein, we report a new, efficient and atom-economical strategy for the synthesis of SCF₃-substituted tryptanthrin derivatives. These previously unreported derivatives were obtained by means of a radical tandem cyclization. The reaction was triggered by addition of a SCF₃ radical to a carbon-carbon double bond and involved the formation of a C(sp³)-SCF₃ bond, a C(sp²)-C bond, and a C(sp²)-N bond. This method has mild conditions and a wide range of substrates which is particularly useful for the preparation of substituted indolquinazoline derivatives that widely exist in many natural products, but are not easy to obtain by conventional approaches.

Nucleophilic trifluoromethylthiolation of bromoalkynones with AgSCF3: C(sp)–SCF3 bond formation towards ynonyl trifluoromethyl sulfides

C(sp)–SCF₃ bond formation via the AgSCF₃ mediated nucleophilic trifluoromethylthiolation of bromoalkynones, delivering various ynonyl trifluoromethyl sulfides in high yields.

N-Heterocyclic Carbene/Lewis Acid Dual Catalysis for the Divergent Construction of Enantiopure Bridged Lactones and Fused Indenes

The chiral triazole carbene and Ti(OPr-i)₄ cocatalyzed reaction between α,β-unsaturated aldehydes and 2-(aroylvinyl)benzaldehydes was systematically studied. A divergence in reaction pathways was observed under different reaction conditions. In benzene solvent and at ambient temperature, the reaction produced 4,5-dihydro-1,4-methanobenzo[c]oxepin-3-ones, the bridged caprolactones, as the major products in moderate yields with excellent enantioselectivity. The same reaction in dichloroethane and at 50 °C, however, gave 2,8-dihydrocyclopenta[a]indenes as the major products in most cases. The application of the method developed was demonstrated by the transformation of the bridged lactone products into enantiopure 4-hydroxy-1,2,3,4-tetrahydronaphthalene-2-carboxylic acids.