Synthesis of Fused Cyclopentenones through Palladium‐Catalyzed Cyclization of 2‐Iodoaryl Allenols

Abstract

A versatile strategy for the synthesis of fused cyclopentenones, key structural motifs in biologically relevant compounds such as indenones and indole alkaloids, has been established successfully through regioselective palladium-catalyzed cyclization of 2-iodoaryl allenols.

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality

“…In this case, 2-iodoaryl allenols 503 and 505 were treated with [(PPh 3 ) 2 PdCl 2 ] and CuI as bimetallic pair, yielding differently substituted fused cyclopentenones 504 and 506 in good yields ( Scheme 85 , reaction b), through a proposed intramolecular Heck-type coupling reaction mechanism. 319 …”

“…Eventual ligand exchange would explain the observed cyclopentenones 497 and return the active metal species to the cycle (Scheme , reaction a, right). , Alcaide and Almendros research group has also contributed to the allenol/cyclopentenone transformation in the context of a cooperative bimetallic catalysis. In this case, 2-iodoaryl allenols 503 and 505 were treated with [(PPh 3 ) 2 PdCl 2 ] and CuI as bimetallic pair, yielding differently substituted fused cyclopentenones 504 and 506 in good yields (Scheme , reaction b), through a proposed intramolecular Heck-type coupling reaction mechanism …”

When Indoles Meet Allene and its Derivatives

“…[53] Interestingly, the presence of a base in the reaction media under similar experimental conditions allowed a switch in the reaction pathway, yielding cyclopentenones 92 through an intramolecular Heck-type process (Scheme 21). [54] Scheme 21. Chemical diversity from indolylallenols.…”

Pentannulation of Heterocycles by Virtue of Precious Metal Catalysis

“…Cyclopenta[b]indole-3(4 H)-ones 22 werep repared through the base-promoted, palladium-catalyzed intramolecular Hecktype cyclization of 3-iodo(indol-2-yl)-a-allenols 21 (Scheme 9). [23] In this transformation the indolylpalladium(II) in-Scheme4.Pd 0 -catalyzed intramolecular cyclization of 8.R eagents and conditions:a )X= I, 5% Pd(OAc) 2 ,1 0% Ph 3 P, 2equiv.TEA, 1 m DMA, 130 8C, 2h; [16] b) X = Br and R 1 ¼ 6 H, 5% Pd(dppf)Cl 2 ,2equiv.K 2 CO 3 ,DMF,130 8C; c) X = Br and R 1 = H, 5% Pd(OAc) 2 ,10% Ph 3 P, 2equiv.CsOAc, DMA, 130 8C. [17] Scheme5.Pd II -catalyzed intramolecular cyclizationo f10.…”

“…Cyclopenta[ b ]indole‐3(4 H)‐ones 22 were prepared through the base‐promoted, palladium‐catalyzed intramolecular Heck‐type cyclization of 3‐iodo(indol‐2‐yl)‐α‐allenols 21 (Scheme ) . In this transformation the indolylpalladium(II) intermediate, formed in the oxidative addition of the Pd 0 to the indole−I bond, underwent an olefin insertion reaction with the proximal allene double bond generating an alkylpalladium intermediate 23 which, after a β‐hydride elimination, gave the product.…”