Cyclization of 1-aryl-4,4,4-trichlorobut-2-en-1-ones into 3-trichloromethylindan-1-ones in triflic acid

Trichloromethyl-substituted enones (1-aryl-4,4,4-trichlorobut-2-en-1-ones, ArCOCH=CHCCl3, CCl3-enones) undergo intramolecular transformation into 3-trichloromethylindan-1-ones (CCl3-indanones) in Brønsted superacid CF3SO3H (triflic acid, TfOH) at 80 °C within 2-10 h in yields up to 92%. Protonation of the carbonyl oxygen of the starting CCl3-enones by TfOH affords the key reactive intermediates, the O-protonated forms ArC(=OH+)CH=CHCCl3, which are then cyclized into the target CCl3-indanones. These cations have been studied experimentally by means of NMR spectroscopy in TfOH and theoretically by DFT calculations. Under the same superacidic conditions in TfOH, CCl3-hydroxy ketones (1-aryl-4,4,4-trichloro-3-hydroxybutan-1-ones; ArCOCH2CH(OH)CCl3) undergo dehydration to the corresponding CCl3-enones, which are further cyclized into CCl3-indanones. The yields of CCl3-indanones starting from CCl3-hydroxy ketones are up to 86% in TfOH at 80 °C within 3-18 h.

A Convergent, Modular Approach to Trifluoromethyl-Bearing 5-Membered Rings via Catalytic C(sp3 )-H Activation

Trifluoromethyl-bearing 5-membered rings are prevalent in bioactive molecules, but modular approaches to these compounds by functionalization of robust C(sp³ )-H bonds in a direct and selective manner are extremely challenging. Herein we report the rhodium-catalyzed α-CF₃ -α-alkyl carbene insertion into C(sp³ )-H bonds of a broad range of substrates to access 7 types of CF₃ -bearing saturated 5-membered carbo- and heterocycles. The reaction is particularly effective for benzylic C-H insertion exerting good site-, diastereo- and enantiocontrol, and applicable to the synthesis of chiral CF₃ analogues of bioactive molecules. Ruthenium α-CF₃ -α-alkyl carbene complexes underwent stoichiometric reactions to give C-H insertion products, lending evidence for the involvement of metal α-CF₃ -α-alkyl carbene species in the catalytic cycle. DFT calculations revealed that the π⋅⋅⋅π attraction and intra-carbene C-H⋅⋅⋅F hydrogen bond elucidate the origin of selectivity of the benzylic C-H insertion reactions.

Enantioselective Synthesis of Bispiro[indanedione-oxindole-cyclopropane]s through Organocatalytic [2+1] Cycloaddition

A series of compounds featuring a novel bispiro[indanedione-oxindole-cyclopropane] moiety have been synthesized through a squaramide-catalyzed [2+1] cycloaddition reaction. The tandem Michael-alkylation reaction of 2-arylidene-1,3-indanediones with 3-bromooxindoles furnished the cycloadducts in high yields with excellent diastereo- and enantioselectivities. The ammonium ylide in the catalytic process, as a key intermediate, was revealed by the high-resolution mass spectrometry study.

4b-Aryltetrahydroindeno[1,2-a]indenes by Acid-Catalyzed Trans­annular Cyclization of Benzannulated Cyclooctene Alcohols

By starting from two simple building blocks, benzannulated cyclooctenones were obtained in three steps. Subsequent Grignard/aryl lithium addition to the ketone yielded the corresponding tertiary alcohols that underwent stereoselective acid-catalyzed transannular cyclization to provide a cis-fused 5/5 bicyclic indanylindane framework exclusively. Subsequent stereoselective nucleophilic addition to the indanyl cation by hydride, water, or electron-rich aromatics furnished the 4b-aryltetrahydroindano[1,2-a]indenes in good to excellent yields (up to 92%) in the trans-C9–C9a form in up to a >99:1 diastereomeric ratio.

Reactions of linear conjugated dienone structures with arenes under superelectrophilic activation conditions. An experimental and theoretical study of intermediate multicentered electrophilic species

Reactions of conjugated dienones with arenes under superelectrophilic activation conditions result in the formation of conjugated enones, indanes, and carbocyclic structures.