Triflic Acid Promoted Transformations of Linear-Conjugated Enynones and their Reactions with Arenes. Synthesis of Dihydropyranones, Conjugated Dienones, and Indanes

Linear-conjugated enynones,1,5-diarylpent-4-en-2-yn-1-ones [Ar-2-CH=CH-C equivalent to C-C(=O)Ar-1], have been cyclized into 2,6-diaryl-2,3-dihydropyran-4-ones in triflic acid TfOH (CF3SO3H). Reactions of these enynones with arenes (ArH)-H-3 in TfOH have afforded, at first stage, products of hydroarylation of the acetylene bond, 1,3,5-triarylpent-2,4-dien-1-ones [Ar-2-CH=CH-C(Ar-3)=CH-C(=O)Ar-1], which have been further cyclized into alkylidene indanes. Plausible reaction mechanisms have been proposed. According to quantum chemical calculations by DFT method, initial key reactive intermediates are vinyl type dications [Ar-2-CH=CH-C+=CH-C(=O+H)Ar-1], generated under the protonation of carbonyl oxygen and acetylene bond of starting enynones in TfOH.

Automated summary

Linear-conjugated enynones were cyclized into alkylidene indanes in triflic acid TfOH. The reactions involved hydroarylation of the acetylene bond followed by further cyclization. Plausible reaction mechanisms were proposed based on DFT calculations.