5-(Alkynyl)dibenzothiophenium Triflates: Sulfur-Based Reagents for Electrophilic Alkynylation

The synthesis of a series of 5-(alkynyl) dibenzothiophenium triflates, prepared from dibenzo[b,d]thiophene 5-oxide and the corresponding trimethylsilyl-substituted alkynes is reported. Their structures were determined by X-ray crystallography, and their reactivities as electrophilic alkynylation reagents evaluated. Their broad substrate scope and functional-group tolerance illustrate their potential to become an alternative to the broadly used EBX reagents. Isotope labeling studies reveal that alkynyldibenzothiophenium salts may undergo attack by nucleophiles at either the alpha- or beta-carbon atom depending on the nature of their substitution pattern. Subsequent elimination of the dibenzothiophene unit and 1,2-migration of one of the groups (in case of beta-attack) affords the desired alkynes.