The First Formation of (1Z)‐1‐Alkylidene‐1H‐isobenzofuranium Amides and 1H‐Inden‐1‐ones: Acid‐Promoted 5‐exo Cyclization and Hydration/Aldol Condensation Reactions of o‐Ethynylbenzophenones

Abstract

1Z)-1-(2,2-Dimethylpropylidene)-1H-isobenzofuranium bis-(trifluoromethylsulfonyl)amides were synthesized through 5exo cyclization reactions between sterically encumbered oalkynylbenzophenones and bis(trifluoromethylsulfonyl)imide (Tf 2 NH). It was confirmed that the five-membered-ring isobenzofuranium amide isomerized to give the corresponding benzopyrylium amide, the six-membered-ring framework compound, in quantitative yield. Treatment of less encum-

Substituent Effect on the Reactions of OsCl2(PPh3)3 with o-Ethynylphenyl Carbonyl Compounds

“…Complex 4c is interesting as it represents a unique example of a structurally characterized metalated isobenzofurfuryl cation. Furfuryl cations are important species that have often been generated in situ and used as reactive intermediates for organic synthesis. , While furfuryl cations have been observed spectroscopically (MS, NMR) and the subject of theoretical studies, to the best of our knowledge, solid-state structures of furfuryl cations have not been reported previously. In addition, 2-furanyl carbene complexes have often been suggested as reactive intermediates in metal-catalyzed reactions of ene-yne-carbonyl compounds.…”

Iodine‐Mediated Cyclization of ortho‐Alkynylaryl Ketones for the Synthesis of Indenone Derivatives

“…2‐Butyl‐3‐phenyl‐1 H ‐inden‐1‐one (2a): Yellow oil (83.7 mg, 79 %). IR (neat) ν̃ = 1703, 1608, 1456, 934, 775, 720, 700 cm –1 .…”

“…Cyclization with the tethered alkyne then results in the regioselective formation of the indenone product (Scheme ) . Moreover, ortho ‐alkynylaryl ketone substrates were also converted into indenone products by using a catalytic amount of NaAuCl 4 · 2H 2 O or a stoichiometric amount of Tf 2 NH . The mode of reaction of these two procedures is the reverse of the previous method: the alkyne moiety is initially activated by these reagents, and then cyclization takes place through the participation of ortho ‐keto moiety (Scheme ).…”

Triflimide (HNTf2) in Organic Synthesis

“…With a similar alkyne protonation as the initiation step, Nagahora, Okuma, and co-workers developed an interesting cyclization of ethynylbenzophenones for the synthesis of indenones . Triflimide is highly efficient in promoting this process under very mild conditions, although its loading was stoichiometric.…”