Lewis Acid Promoted Reactions of 1,1-Diarylallenes and Ketone Derivatives: Synthesis of Indenes by an Addition/Cyclization Reaction

Abstract

The Lewis acid promoted reaction of 1,1-diarylallenes with ketone derivatives was examined. The tin(IV) chloride promoted reaction of diarylallenes with vinyl ketones gave indene derivatives through a conjugate addition/cyclization reaction. The reaction of diphenylallene with diethyl oxomalonate in the presence of one equivalent of tin(IV) chloride at -40 °C gave diethyl hydroxy(3-phenyl-1H-inden-2-yl)malonate as the major product through a carbonyl addition/cyclization reaction, whereas the same reactants in the presence of 0.2 equivalents of tin(IV) chloride at 80°C gave diethyl (3-phenyl-1H-inden-2-yl)malonate. Diethyl hydroxy(3-phenyl-1H-inden-2-yl)malonate was also converted into the latter product on heating at 80 °C in the presence of 0.2 equivalents of tin(IV) chloride.

CoIII–Carbene Radical Approach to Substituted 1H-Indenes

“…A series of intermolecular approaches have also been developed for indene synthesis, including [3 + 2] annulation of aryl alkynes with benzyl derivatives, carbonyls, allenes and dienophiles, palladium-catalyzed carbocyclization of aryl halide/boronic acids and alkynes, Fe-catalyzed cyclization of benzyl and substituted alkynes and allenes, noble metal catalyzed aromatic C–H bond activation cyclization, and copper catalyzed radical cyclizations . However, several of these existing methods suffer from functional group intolerance, the necessity of expensive (noble) transition metal catalysts, harsh reaction conditions and/or are limited to the synthesis of specific indenes with a particular substitution pattern.…”

Recent Advances in the Synthesis of Indanes and Indenes

“… Synthesis of functionalized indenes 218 from diarylallenes 217 and vinyl ketones by SnCl 4 ‐promoted sequential conjugate addition‐FC cyclization …”

“…Interestingly, when the reaction was carried out at −78 °C or RT followed by treatment with Et 3 N, γ‐lactone derivatives were selectively formed instead of indenes . In a similar process, 1,1‐diarylallenes 217 reacted with vinyl ketones in DCM or CHCl 3 at RT and the presence of 1 equiv of SnCl 4 to afford the corresponding indene derivatives 218 in moderate yields (Scheme ) . The same reaction, performed with diethyloxomalonate as the ketone partner, led to diethyl hydroxyl(3‐aryl‐1 H ‐inden‐2‐yn)malonates or the reduced products, (3‐aryl‐1 H ‐inden‐2‐yn)malonates, depending on reaction conditions …”