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 α- or β-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 β-attack) affords the desired alkynes.