Reactivity of 5-(Alkynyl)dibenzothiophenium Salts: Synthesis of Diynes, Vinyl Sulfones, and Phenanthrenes.

The reactivity of 5-(alkynyl)dibenzothiophenium salts 1 is explored in the presence of different nucleophiles, dienes, and under photochemical conditions. Reaction with lithium acetylides affords diynes in moderate yields; while depending on the substitution pattern, the reaction with sulfinates delivers either the alkyne transfer products, alkynyl sulfones, or ß-(sulfonium) vinyl sulfones through addition to the C-C triple bond. Similar behavior is observed when tosylamines are used as nucleophiles. Salts of general formula 1 also react with dienes to render the corresponding Diels-Alder cycloadducts. The vinyl sulfonium salts obtained by these routes further react with nucleophiles through a Michael addition, dibenzothiophene elimination sequence. Alternatively, they also engage in photoinduced radical cyclizations to produce substituted phenanthrenes. Attempts to use this specific addition/radical cyclization sequence for the construction of the 6a,7-dehydroaporphine skeleton present in several families of alkaloids are also described.

Protein Conjugation by Electrophilic Alkynylation Using 5-(Alkynyl)dibenzothiophenium Triflates.

5-(Alkynyl)dibenzothiophenium triflates are introduced as new reagents to prepare different protein conjugates through site-selective cysteine alkynylation. The protocol developed allows a highly efficient label of free cysteine-containing proteins with relevant biological roles, such as ubiquitin, the C2A domain of Synaptotagmin-I, or HER2 targeting nanobodies. An electrophilic bis-alkynylating reagent was also designed. The second alkynylating handle thus introduced in the desired protein enables access to protein-thiol, protein-peptide, and protein-protein conjugates, and even diubiquitin dimers can be prepared through this approach. The low excess of reagent needed, mild reaction conditions used, short reaction times, and stability of the S-C(alkyne) bonds at physiological conditions make this approach an interesting addition to the toolbox of classical, site-selective cysteine-conjugation methods.

Polymorphism of bis-(1,3-benzo-thia-zol-2-yl) tri-thio-carbonate.

The polymorphism of the title compound, C15H8N2S5, is reported, in which the (syn,syn) and (syn,anti) conformers simultaneously crystallized from a chloro-form solution. The complete mol-ecule of the (syn,syn) form is generated by a crystallographic twofold axis. The geometries of both conformers are compared in detail, revealing no significant differences in bond lengths, despite different bond angles because of the conformational changes. Analysis of the inter-molecular inter-actions, aided by Hirshfeld surfaces, shows distinctive S⋯S and S⋯N contacts only for the (syn,anti) conformer. Aromatic π-π-stacking inter-actions are found for both conformers, which occur for the (syn,anti) conformer between pairs of mol-ecules, but are continuous stacks in the (syn,syn) conformer. Non merohedral twinning was found for the crystal of the (syn,anti) conformer used for data collection.

Synthesis, Structure, and Reactivity of 5-(Aryl)dibenzothiophenium Triflates.

A synthetic protocol for the preparation of 5-(aryl)dibenzothiophenium salts starting from inexpensive dibenzothiophene S-oxide and simple arenes is reported. The scope of the method regarding the nature of the arene is evaluated, intermediates along the reaction sequence have been trapped, and side-reactions identified. In addition, the X-ray structures of a complete set of these salts are reported and their reactivities studied. Specifically, chemoselective Suzuki coupling is observed at the dibenzothiophenium in the presence of iodides.