Phosphine-Catalyzed (3 + 2)/(3 + 2) Sequential Annulation of γ-Vinyl Allenoates: Access to Fused Carbocycles

Abstract

The first (3 + 2)/(3 + 2) sequential annulation of γ-vinyl allenoates with alkylidenemalononitriles enabled by phosphine catalysis has been reported. A broad range of structurally dense tetra- and penta-substituted bicyclic­[3,3,0]­octene derivatives, containing a quaternary center and three sequential stereogenic center, were synthesized in good to excellent yields. In this approach, three new C–C bonds are formed in one pot, and εC and αC of γ-vinyl allenoate are two electrophilic centers, whereas its γC exhibits nucleophilic reactivity.

Construction of CF3-Containing Tetrahydropyrano[3,2-b]indoles through DMAP-Catalyzed [4+1]/[3+3] Domino Sequential Annulation

“…There has been no report on the addition of nucleophiles to the γ position of intermediate B , for there is no empty orbital in the ammonium ion of intermediate B to stabilize the carbon anion in the subsequently generated ammonium ylide (Scheme b) . To overcome the limitations, and on the basis of our group’s previous work in the exploration of novel reaction modes of β′-acetoxy allenoate and sequential annulations in organocatalysis to construct the polycycles, we envisioned that the DMAP (4-dimethylaminopyridine) would provide a π-system and make it a more stable corresponding ylide intermediate through a p-π conjugation between the carbon anion and the aromatic ring of DMAP. Herein, we sought to use o -aminotrifluoroacetophenone derivatives as electron donor–acceptor compounds to realize a DMAP-catalyzed [4+1]/[3+3] domino annulation for the efficient formation of a CF 3 -containing tetrahydropyrano­[3,2- b ]­indole system (Scheme c).…”

Phosphine-Catalyzed Sequential [3 + 2]/[3 + 2] Annulation between Allenoates and Arylidenemalononitriles for the Enantioselective Construction of Bicyclo[3,3,0]octenes and Cyclopenta[c]quinolinones

“…It is worth noting that even though such an idea may appear to be simple and straightforward, such an approach has never been adopted to build up bicylic carbocycles . Herein, we report the first diastereo- and enantioselective phosphine-catalyzed sequential [3 + 2]/[3 + 2] annulation of allenoates with arylidenemalononitriles for the facile synthesis of cis -fused bicyclic­[3,3,0]­octene scaffolds, followed by selective reduction/cyclization to furnish highly enantiomerically enriched cyclopenta­[ c ]­quinolinones …”

Diastereoselective Synthesis of Bicyclo[3.3.0]octenones by Copper-Catalyzed Transannular Ring-Closing Reaction

“…In particular, the bicyclo[3.3.0] ring skeleton is a key framework in many pharmaceuticals and natural products, such as merrilactone A, xialenon A 1, xestenone, , and chloriolin-A (Figure ). , Generally, the synthetic methodologies for bicyclic compounds include cycloaddition , or annulation reactions, which are well-documented in the literature. Another efficient and step-economical method is transannular ring contraction .…”