Benzene construction via Pd-catalyzed cyclization of 2,7-alkadiynylic carbonates in the presence of alkynes

Abstract

A palladium-catalyzed highly regio- and chemo-selective cyclization to construct 1,3-dihydroisobenzofuran and isoindoline derivatives under mild conditions has been developed.

Palladium‐Catalyzed Triple Cyclization of 2,7‐Alkadiynylic Carbonates with 2‐Butyne‐1,4‐diol or 2‐Butyne‐1,4‐disulfonamides

“…Nowadays, palladium‐catalyzed cyclization of propargyl alcohol derivatives with unsaturated hydrocarbons such as alkenes, alkynes, and allenes has been a powerful tool to prepare polycycles . Recently, our group developed an efficient benzofuran construction via a Pd‐catalyzed intermolecular annulation of 2,7‐alkadiynylic carbonates with functionalized terminal alkynes (Scheme a) . We assumed that if the R group at 8‐position is replaced with an ester group, the newly designed 2,7‐alkadiynylic carbonates may react with symmetric internal alkynes such as 2‐butyne‐1,4‐diol or 2‐butyne‐1,4‐disulfonamides to form tricyclic compounds with an extra lactone or lactam unit (Scheme b).…”

“…On the basis of our experimental results, we proposed two possible mechanism routes as shown in Scheme by taking the reaction of 4 a and 5 a as an example. For the intermolecular process , oxidative addition of 4 a with Pd(0) would afford the allenylpalladium IN‐1 , which undergoes intramolecular insertion of the triple bond to generate the alkenylpalladium species IN‐2 –. The species IN‐2 would undergo intermolecular syn ‐carbopalladation of the C≡C bond of 5 a to produce a new alkenylpalladium intermediate IN‐3 .…”

“…For the intermolecular process , oxidative addition of 4 a with Pd(0) would afford the allenylpalladium IN‐1 , which undergoes intramolecular insertion of the triple bond to generate the alkenylpalladium species IN‐2 –. The species IN‐2 would undergo intermolecular syn ‐carbopalladation of the C≡C bond of 5 a to produce a new alkenylpalladium intermediate IN‐3 . Then intramolecular carbopalladation of allene would form a new benzylpalladium intermediate IN‐4 , which finally form the tricyclic product 6 aa after the β‐H elimination and lactonization in the presence of NEt 3 .…”

Palladium Nanoparticles Supported on Smopex-234® as Valuable Catalysts for the Synthesis of Heterocycles

“…Owing to their great importance, there has been a continuous interest in developing new and efficient methods for the synthesis of such heterocycles. Several procedures are based on the palladium-promoted cyclization of suitable substrates, such as benzaldehydes [56], benzyl [57][58][59][60] and homobenzyl alcohols [61,62], propargyl ethers [63][64][65][66][67][68], benzylethers [58] and benzylamines [69], anilines [70], propargylamides [71], and arylimides [72].…”

Construction of Benzopolycycles via Pd-Catalyzed Intermolecular Cyclization of 2,7-Alkadiynylic Carbonates with Terminal Propargyl Tertiary Alcohols

“… For example, concentricolide is a compound with in vitro activity against HIV-1 and furanclausamine A as well as B have anti-bacterial activity. , These types of skeletons were commonly constructed from linear triynes: (1) the intramolecular Hexadehydro-Diels–Alder (HDDA) reaction of 1,3,8-triynes forms aryne intermediates, which subsequently react with nucleophiles to produce tricyclic molecules (Scheme a); , (2) the transition metal-catalyzed intramolecular [2 + 2 + 2] cyclization of 1,6,11-triynes (Scheme b). , In addition, tandem reactions consisting of oxidative addition, consecutive carbopalladation, and eventual Heck process of alkenyl halides with diynes were also efficient routes to benzopolycycles . Recently, our group developed an efficient process of benzofuran construction via a Pd-catalyzed intermolecular annulation of 2,7-alkadiynylic carbonates with alkynes (Scheme c) . Interestingly, when we applied propargyl tertiary alcohols to this reaction, the chemoselectivity was unexpectedly different: tricyclic skeletons could be easily constructed via the intramolecular nucleophilic attack of oxygen anion instead of the β-H elimination.…”