Transformations of Conjugated Enynones in the Superacid CF₃SO₃H. Synthesis of Butadienyl Triflates, Indanones, and Indenes

Abstract

Conjugated 1,5-diarylpent-2-en-4-yn-1-ones add the superacid CF3SO3H to the acetylenic bond with formation of the corresponding butadienyl triflates. Under superacidic reaction conditions, these triflates are transformed into indanone or indene derivatives depending on which substituents on the aromatic ring are conjugated with the butadiene fragment. In a less acidic system (10% vol pyridine in CF3SO3H) only the formation of butadienyl triflates takes place. Cationic reaction intermediates were studied by means of NMR and DFT calculations.

Superacidity of P(OH)3 and SO(OH)2 derivatives of cyclopentadiene and vinylcyclopentadiene in the gas phase: A computational DFT analysis

“…Although the chemistry of acids and bases is well known, this research field is still very active because of an increased demand for new compounds with higher acidity. Superacids are important reagents in chemistry due to their applications as catalysts in a great variety of transformations in the chemical industry and synthesis of organic compounds . Therefore, in past decades much research interest has been devoted to the design, synthesis and assessment of highly acidic materials.…”

“…Superacids are important reagents in chemistry due to their applications as catalysts in a great variety of transformations in the chemical industry [5][6][7] and synthesis of organic compounds. [8][9][10][11][12][13] Therefore, in past decades much research interest has been devoted to the design, synthesis and assessment of highly acidic materials. This holds, in particular, for neutral organic superacids, since they possess a number of distinct advantages over their mineral (inorganic) counterparts in solution, being reactive in mild chemical environments.…”

Stereoselective Construction of (E,Z)‐1,3‐Dienes and Its Application in Natural Product Synthesis

“…Initially used by Nakagawa in 1977, [228] the 1,6‐addition of nucleophiles to 4‐yn‐2‐en‐one derivatives is an efficient method for constructing conjugated Z,E ‐dienes; however, they exhibit variable Z selectivities [229–233] . Furthermore, Ooi described in 2018 a spectacular organocatalysed 1,6‐Michael addition of azlactones ( 235 ) to enynyl N ‐acyl pyrazoles ( 236 ) [234] .…”

“…however, they exhibit variable Z selectivities. [229][230][231][232][233] Furthermore, Ooi described in 2018 a spectacular organocatalysed 1,6-Michael addition of azlactones (235) to enynyl N-acyl pyrazoles (236). [234] The use of a P-spiro chiral triaminoiminophosphorane catalyst not only allows the perfect control of the addition regioselectivity (1,6 vs 1,4), but also the Z,Econfiguration of the diene and the enantioselectivity of the quaternary centre in the resulting compounds (237, Scheme 92).…”

Brønsted Acid Promoted Cyclization of Cross‐Conjugated Enynones into Dihydropyran‐4‐ones

“…Superelectrophilic activation makes it possible to form cationic species of enhanced reactivity, and this requires their relative stabilization, typically by delocalization of the positive charge over conjugated systems We have shown recently that diaryl‐substituted conjugated enynones, in particular 1,5‐diarylpent‐2‐en‐4‐yne‐1‐ones, are suitable structures for access to vinyl triflates, indanones, and indenes under superelectrophilic activation . Clearly, the reactivity of an enynone depends on the relative positions of the three functional groups (C=O, C=C, and C≡C), and we decided to study the behavior of systems in which the carbonyl group is cross‐conjugated between the double and the triple bonds (i.e., cross‐conjugated enynones).…”