Palladium-Catalyzed Formal (5 + 2) Annulation between ortho-Alkenylanilides and Allenes

Abstract

2-Alkenyltriflylanilides react with allenes upon treatment with catalytic amounts of Pd(OAc) and Cu(II) to give highly valuable 2,3-dihydro-1H-benzo[b]azepines, in good yields, and with very high regio- and diastereoselectivities. Density functional theory (DFT) calculations suggest that the C-H activation of the alkenylanilide involves a classical concerted metalation-deprotonation (CMD) mechanism.

Recent Advances in Transition‐Metal‐Catalyzed Oxidative Annulations to Benzazepines and Benzodiazepines

“…Then, coordination (II) and migratory insertion of the 1,3-diene forms an eight-membered palladacycle III, which is further stabilized with the second double bond of the diene (Pd σ-allyl complex). Simultaneously, the groups of Mascareñas/Gulías [39] and Zeng [40] reported a Pd-catalyzed (5 + 2) annulation of ortho-alkenylanilides 9 (triflamides or tosylamides) and allenes 10 to give 3-alkylidene 1-benzazepines 11 (Scheme 4). Mechanistic studies supported by DFT calculations suggested the initial formation of a sixmembered palladacycle I through a CÀ H bond activation (via CMD).…”

“…1-Benzazepines have been synthesized under Pd catalysis using nitrogenated substrates bearing L-Type (amines) and X-Type (amides) DGs via multicomponent and standard annulations. [35][36][37][38][39][40] They have been also synthesized under Ir catalysis in a (5 + 2) annulation of o-alkenylanilines and allyl carbonates. [41] In addition, a Rh-catalyzed (6 + 1) carbonylation of Ncyclopropylanilides (carbonylative CÀ C activation) rendered benzazepin-5-ones ( Figure 3).…”

“…1‐Benzazepines have been synthesized under Pd catalysis using nitrogenated substrates bearing L‐Type (amines) and X‐Type (amides) DGs via multicomponent and standard annulations [35–40] . They have been also synthesized under Ir catalysis in a (5+2) annulation of o ‐alkenylanilines and allyl carbonates [41] .…”

Recent Developments in the [5+2] Cycloaddition

“…As an extension of these works (Scheme 38), [82] Gulias and Mascarenas developed related reactions involving ortho-vinylanilides, in 2017. [83] Indeed, ortho-vinylanilides 136 reacted with allenes 128 in the presence of 5 mol% of Pd(OAc) 2 combined with 50 mol% of Cu(OAc) 2 and two equivalents of triethylamine in acetonitrile at 82 8 8C to give the corresponding [5+2] cycloadducts 137 in moderate to high yields (40-92%), as illustrated in Scheme 39. A wide variety of these highly valuable 2,3-dihydro-1H-benzo[b]azepines was achieved starting from either 1,1disubstituted symmetrical allenes, such as dimethyland diphenylallenes, cyclic allenes, non-symmetrical allenes or trisubstituted allenes which all provided good yields.…”

Temperature-Controlled Divergent Hydroamination Cyclization [2+2]-Cycloaddition Cascade Reactions of Homopropargylic Amines with 2-Butynedioates: Direct Access To Pyrrolo-b-cyclobutene and Dihydro-1H-azepines

“…Among them, the intermolecular [5+2]-cycloaddition reactions are commonly used . For example, Mascarenas’s group reported a palladium-catalyzed formal [5+2]-annulation between ortho -alkenylanilides and allenes to prepare 2,3-dihydro-1 H -benzo­[ b ]­azepines (Scheme a) . Zhang and co-workers developed a rhodium­(I)-catalyzed intermolecular [5+2]-cycloaddition of vinyl aziridines and alkynes to access nitrogen heterocycles (Scheme b) .…”