Dimerization of Aromatic Terminal Alkynes Featuring Hydrophilic Functional Groups under Ruthenium and Acid Promoted Catalysis. Competitive Alkyne Hydration upon Substituent Effect

The self-coupling (hydroalkynylation) process of aromatic terminal alkynes RC6H4CCH to give dimeric 1,4-diaryl-1-en-3- yne products (trans-RC6H4CCCH=CHC6H4R) is catalyzed by the complex [{RuCl(?-Cl)(?6-p-cymene)}2] with sodium acetate cocatalyst dissolved in neat acetic acid, the reaction proceeding with high trans-stereoselectivity under mild conditions (r.t.) even for substrates with protic or polar substituent groups (e.g.R=3-OH, 4-CH2OH, 4-NHAc, -CHO, 4-tetra-O-acetyl-?-D-glucopyranoside). In presence of strongly electron donating arene substituents, NMe2 and NH2, the triple bond is activated toward exclusive triple bond hydration by reaction with acetic acid at room temperature also in absence of the ruthenium catalyst.