An Efficient Synthesis of Benzazocines by Gold(I)‐Catalyzed Tandem 1,2‐Acyloxy Shift/[3+2] Cycloaddition of Terminal 1,9‐Enynyl Esters

Abstract

An effective synthesis of structurally diverse benzazocines was accomplished in good to excellent chemical yields (55-82 %) through a gold(I)-catalyzed cascade reaction involving tandem 1,2-acyloxy shift/[3+2] cycloaddition of terminal 1,9-enynyl esters. The reaction proceeds under extremely mild conditions and represents one of the relatively few transition-metal-catalyzed intramolecular cycloaddition reactions for the synthesis of benzazocines.

Construction of Medium-Sized Rings by Gold Catalysis

“…The transformation shown in Scheme 35 only works for Z-conjugated terminal dienes. Xie and co-workers 156 replaced the internal alkene in 135 with aryl moieties, such as styrene units, Scheme 36, and further expand the utilities to the corresponding nitrogen-containing counterparts in 140. Thus, a selection of 1,9-enynyl esters underwent the cascade reaction to give the substituted eight-membered nitrogen heterocycle benzazocine derivatives 141.…”

“…Construction of medium-sized ring ethers and aza-heterocycles through a sequential cascade reaction involving a gold-catalyzed cycloisomerization coupled with cycloaddition was developed by Xie, She, and co-workers. − On the basis of their initial report on a cascade reaction that proceeds through 1,2-acyloxy migration/[3 + 2] cycloaddition of enynyl esters, She and co-workers developed an Au­(I)-catalyzed 1,2-acyloxy migration of dieneyne derivatives such as 135 generating a gold carbene species 136 , Scheme . Carbonyl lone pair addition to the latter then gives a 1,3-dipole trapped with an internal alkene via an intramolecular [3 + 2] cycloaddition, 137 to 138 , leading to formation of a tricyclic acetal 138 which upon hydrolysis affords compound 139 with an eight-membered ether ring decorated with two ketonic functionalities.…”

Recent Advances in the Synthesis of Hydrogenated Azocine-Containing­ Molecules

“…The reaction proceeded under mild conditions leading to benzoazocines 317 in good to excellent yields of 55–82% (Scheme 92 ). 98…”

Gold-Catalyzed Homogeneous (Cyclo)Isomerization Reactions

“…These 64 species engage in a [3+2] cycloaddition reaction involving the terminal alkene to afford the polycyclic scaffolds 65 , which convert into the final substituted benzocines 66 by a hydrolisis process. Two different diastereoisomers were isolated and fully characterized, the trans isomers 66 being the major products of the reaction (Figure 6B) (Feng et al, 2016). The same group has reported on the successful attempts to obtain complex tetracyclic frameworks by appliying a similar gold-catalyzed protocol on related linear enynyl esters (Sun et al, 2017).…”