Synthesis of Indenes via Brønsted Acid Catalyzed Cyclization of Diaryl- and Alkyl Aryl-1,3-dienes

Abstract

Substituted indenes can be synthesized via the Brønsted acid catalyzed cyclization of diaryl- and alkyl aryl-1,3-dienes. In this approach, treatment of symmetric or unsymmetric diaryl- and alkyl aryl-1,3-dienes with a catalytic amount of trifluoromethanesulfonic acid gives a variety of indene derivatives in good to excellent yields under mild conditions.

Nazarov Cyclization of Divinyl and Arylvinyl Epoxides: Application in the Synthesis of Resveratrol‐Based Natural Products

“…After having confirmed Nazarov cyclization pathway,f urther substrate scope and versatility of this method was intended in the synthesis of indenes since they are important scaffolds not only in the bioactive natural products but also in medicinal and materials chemistry. [22] We observed, arylvinyl epoxides are more reactive in comparison to divinyle poxides.I ng eneral, the reaction tolerated aw ide range of epoxides 2aa-ao,a nd reactingw ith 0.3 equivalents of BF 3 ·OEt 2 afforded indenes in good to excellent yield (Table 3). Initially, indenes could not be obtained in satisfactory yields and in some cases chloride addi-tion at b to epoxide was observed when arylvinyl epoxides reacted with 1 m TiCl 4 ,e ven thoughi tw as the most effective with divinylepoxides.…”

Recent Advances in the Synthesis of Indanes and Indenes

“…Aryl‐1,3‐dienes undergo intramolecular FC alkylation when treated with a Brønsted or Lewis acid to give indenes . In a recent paper, a variety of substituted indenes 213 were easily synthesized in good to excellent yields by treating diaryl‐ and alkyl aryl‐1,3‐dienes 212 with trifluoromethanesulfonic acid under mild conditions (DCM, 0–70 °C, 5–30 min) . The process took place by protonation of the diene system followed by EAS (Scheme )…”

“… Synthesis of substituted indenes 213 by intramolecular FC alkylation of 212 induced by trifluoromethanesulfonic acid …”

Ene-yne Cross-Metathesis for the Preparation of 2,3-Diaryl-1,3-dienes

“…Among them, ruthenium-catalyzed addition of aldehydes [5] and olefin metathesis [6], nickel-catalyzed multicomponent coupling with alkynes or aldehydes and dimethylzinc in the presence of carbon dioxide [7,8], rhodium-catalyzed asymmetric [4 + 3] cycloaddition with vinylcarbenoids [9], palladium-catalyzed telomerization with various nucleophiles [10][11][12], hydroamination [13,14] and hydroamidocarbonylation [15], are representative examples. However, monoarylated 1,3-dienes have been used for triflic acid-catalyzed synthesis of indenes [16], ruthenium-catalyzed isomerization [17], palladium-catalyzed hydroarylation with boronic esters [18], cobalt-catalyzed hydrosilylation [19], asymmetric hydrovinylation with ethylene [20] and enantioselective cycloaddition with internal alkynes [21]. 2-Aryl-and 2,3-diaryl-dienes of type A have been extensively studied for the access to cyclic products resulting from Diels-Alder [4,22] They have also been recently involved in iridium-catalyzed hydrohydroxymethylation [25] and ruthenium-catalyzed hydroxymethylation [26].…”

“…The few reported methods rely on palladium-catalyzed cross-coupling of p-tolyl iodide with 3-silyl-3-phenylbuta-1,3-diene in 40% yield [39] and styryl triflates with styryl boronates [40]. An unsymmetrical 2,3-bis(2-nitrophenyl)-1, 3-butadiene derivative has been prepared in 61% yield by a Pd-catalyzed Stille cross-coupling [41], whereas the tentative cross-coupling of two different hydrazones led to modest yields in the unsymmetrical product besides the symmetrical ones [16]. Because it is a straightforward atom economic reaction, ene-yne cross metathesis has been applied as an efficient method for the construction of 1,3-dienes [4,[42][43][44][45].…”