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

A new benzannulation reaction with accompanied trifluoromethylthiolation is described. This benzannulation can generate a range of trifluoromethylthiolated benzolactams and benzolactones from 1,3,8-triynes and a stoichiometric amount of AgSCF3 at 90 °C through an initial Alder-ene reaction, 1,4-addition of AgSCF3, and a series of bond-reorganization processes that include double bond migration, 6π-electrocyclization, and a [1,3]-H shift. For certain substrates containing a triisopropylsilyl (TIPS) group, the final [1,3]-H shift-interrupted products, were obtained.

Hydrohalogenative aromatization of multiynes promoted by ruthenium alkylidene complexes.

A new functionalization method of arynes promoted by a novel catalytic role of the Grubbs-type ruthenium alkylidene complex is described. Through a sequence of aryne formation followed by their halo-functionalization, various bis-1,3-diynes were directly converted to functionalized aryl chlorides, bromides and iodides in good yields in the presence of a catalytic amount of a ruthenium alkylidene complex and halogenated hydrocarbons such as CH2Cl2, CHCl3, CH2Br2, and CH2I2. The utility of this novel transformation is demonstrated by a formal synthesis of herbindole B.

Hydroarylation of arynes catalyzed by silver for biaryl synthesis.

A new biaryl synthesis via silver-catalyzed hydroarylation of arynes from acyclic building blocks with unactivated arenes in intra- and intermolecular manners has been developed. The previously observed Diels-Alder reactions of arynes with arene were not observed under the current silver-catalyzed conditions. Deuterium scrambling and DFT calculations suggest a stepwise electrophilic aromatic substitution mechanism through the formation of a Wheland-type intermediate followed by a water-catalyzed proton transfer in the final step of the hydroarylation.

Alder-ene reactions of arynes.

Efficient Alder-ene reactions of various arynes generated directly from bis-1,3-diynes are described. The reactivity of ene donors with different tethers was examined under thermal and metal-catalyzed conditions, which indicates that both the formation of aryne intermediates and their ene reactions are less sensitive to the catalyst than to the structural features of the substrates.

Alkane C-H insertion by aryne intermediates with a silver catalyst.

Arynes generated directly from alkyne building blocks in the presence of silver catalysts effectively activate primary, secondary, and tertiary alkane C-H bonds. This C-H insertion requires only a catalytic amount of silver complex and modest heating compared to harsh conditions and extra promoters including directing groups, oxidants, and bases in typical transition-metal-based C-H bond functionalizations. Preliminary mechanistic studies suggest that the C-H bond-breaking and new bond-forming events take place in a concerted manner, rendering a formal 1,2-addition of C-H bond across the π-bond of arynes.

Subtle electronic effects in metal-free rearrangement of allenic alcohols.

A general and stereoselective rearrangement of allenic alcohols to (E,E)-1,3-dien-2-yl triflates and chlorides was developed under metal-free conditions. Subtle electronic effects of the alkyl and aryl substituents on the carbon bearing the hydroxyl group has a profound impact on the reaction rate and efficiency such that vinyl triflates were obtained from electron-deficient substrates and trimethylsilyl triflate whereas vinyl chlorides were generated with an electron-rich substrate and trimethylsilyl chloride.