Cyclization of 1-Aryl-5-Phenylpent-4-en-2-yn-1-Ones to 2,3-Dihydropyran-2-Ones in Trifluoromethanesulfonic Acid

Hemicurcuminoids (1-styryl-1,3-diketones) – valuable multi-faceted building blocks for organic synthesis

“…Thus, an assumption was made that formation of each dihydropyranone they obtained proceeds through the corresponding pentanedione intermediate (Scheme 40). However, recently, an analogous reaction has also been reported by Zalivatskaya et al , 57,58 who performed it with TfOH and proposed an alternative mechanism for the formation of dihydropyranones 56 : enediones are by-products and the reaction proceeds through the formation of a C-1 charged cation intermediate.…”

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

“…Longer reaction time has finally led to cyclization of species E (in its resonance form E′ ) into dihydropyranones 3 through an intermediate formation of species G and F . See also a detailed discussion on mechanism of such dihydropyranone formation in our previous studies [11,13] and in works [17,18] …”

“…It was found that enynones 1 a , f , c , d were cyclized into 2,3‐dihydropyran‐4‐ones 3 a – d correspondingly in excess of TfOH at room temperature for 1 h (Scheme 3, see also our preliminary communication [13] ). The position of the double bond in dihydropyranone structures 3 a – d was confirmed by NOESY correlations between vinyl proton and ortho ‐protons of neighbor aromatic system (see SI).…”

“…There are just a few examples of reactions of these enynones with nucleophiles, [6–7] and their intramolecular cyclization into various carbocycles [8] . Based on our recent studies on reactions of other types of linear‐ and cross‐conjugated enynones under the superelectrophilic activation conditions [9–12] and on our short preliminary communication on the cyclization of 1‐aryl‐5‐phenylpent‐4‐en‐2‐yn‐1‐ones into 6‐aryl‐2‐phenyl‐2,3‐dihydropyran‐4‐ones in triflic acid TfOH (CF 3 SO 3 H), [13] we undertook a special investigation on TfOH‐promoted transformations of the series of 1,5‐diarylpent‐4‐en‐2‐yn‐1‐ones.…”