Diastereoselective and Enantioselective Synthesis of Barbiturate-Fused Spirotetrahydroquinolines via Chiral Palladium(0)/Ligand Complex Catalyzed [4 + 2] Cycloaddition of Vinyl Benzoxazinanones with Barbiturate-Based Olefins

Abstract

Under the catalysis of chiral palladium(0)/ligand complex, the [4 + 2] cycloaddition between vinyl benzoxazinanones and barbiturate-based olefins proceeded readily and provided barbiturate-fused spirotetrahydroquinolines in up to 96% chemical yield with up to >99:1 dr and 97% ee. The absolute configuration of barbiturate-fused spirotetrahydroquinolines was clearly identified by X-ray single crystal structure analysis. The reaction mechanism was proposed to shed light on the enantioselective formation of barbiturate-fused spirotetrahydroquinolines.

An Update of Transition Metal-Catalyzed Decarboxylative Transformations of Cyclic Carbonates and Carbamates

“…For instance, the decarboxylative formation of dihydroquinazolinones through a Pd-catalyzed [4 + 2] cycloaddition using sulfonyl isocyanates as electrophiles was reported by Shi and co-workers [10]. With the introduction of cyclic imines or barbiturate-based olefin reactants, it is feasible to construct highly functionalized quinazolines through decarboxylative cycloadditions [11][12][13]. Most recently, the annulation of deconjugated butenolides or azlactones with vinyl carbamates towards highly functionalized chiral dihydroquinol-2-ones was released by the Xiao group [14].…”

Advances in Palladium‐Catalyzed Decarboxylative Cycloadditions of Cyclic Carbonates, Carbamates and Lactones

“…Soon after, asymmetric decarboxylative [4+2] cycloadditions of 4‐vinyl benzoxazinanones 108 with various electron‐deficient alkenes were successively disclosed for constructing the important chiral tetrahydroquinoline derivatives. In 2018, Zhao and coworkers reported asymmetric DCs of 108 with barbiturate‐derived olefins 42 , affording the barbiturate‐fused spirotetrahydroquinolines 117 in excellent results with chiral palladium complex as catalyst (Scheme 57, eq 1) [39a] . Notably, replacing the methyl group on nitrogen of 42 with H resulted in a failure for the reaction.…”

Recent Advances in Metal‐Catalyzed Decarboxylative Reactions of Vinyl Benzoxazinanones

“…To account for the enantioselective formation, the author predicted a reaction mechanism for the [4+2] cycloaddition between 1 and 28 as depicted in (Scheme 13). [15] Both pathway A and pathway B include a reversible aza‐michael addition and an intramolecular cyclization sequence. Catalysed by in situ formation of chiral Pd(0)/ L1 complex, 1 decarboxylates into a chiral Pd‐stabilized zwitterionic intermediate III .…”