Alkyne Carbonyl Metathesis As a Means To Make 4‑Acyl Chromenes: Syntheses of (±)-Deguelin and (±)-Munduserone

A highly convergent synthetic approach to rotenoid natural products is described. Successful pairing of two building blocks for Sonogashira cross-coupling and intramolecular alkyne carbonyl metathesis allows ready access to 4-acylchromene, a key substructure of these natural products, leading to syntheses of (±)-deguelin and (±)-munduserone in high overall yields

Altering the Cyclization Modes: Temperature-Dependent Intramolecular 7-<i>Endo-Dig</i> vs 6-<i>Endo-Dig</i> Electrophilic Ring Closures

In an attempt to construct 10-acyl-5<i>H</i>-benzo­[<i>e</i>]­pyrrolo­[1,2-<i>a</i>]­azepines via acid-catalyzed intramolecular alkyne carbonyl metathesis, two distinctive modes of cyclization were revealed to depend on the reaction temperatures. 5<i>H</i>-Benzo­[<i>e</i>]­pyrrolo­[1,2-<i>a</i>]­azepine-1-carbaldehydes with a substituent at the C11 position were obtained as major products at 90 °C as a result of intramolecular 7-<i>endo-dig</i> cyclization, while 6-<i>endo-dig</i> ring closure by electrophilic addition of nitrogen of the pyrrole to a vinyl cation generated under acidic medium followed by an unprecedented domino rearrangement process was observed at 40 °C in some cases, resulting in 5-aryl-11<i>H</i>-benzo­[<i>d</i>]­pyrrolo­[1,2-<i>a</i>]­azepine-1-carbaldehydes along with the former products

Altering the Cyclization Modes: Temperature-Dependent Intramolecular 7-<i>Endo-Dig</i> vs 6-<i>Endo-Dig</i> Electrophilic Ring Closures

In an attempt to construct 10-acyl-5<i>H</i>-benzo­[<i>e</i>]­pyrrolo­[1,2-<i>a</i>]­azepines via acid-catalyzed intramolecular alkyne carbonyl metathesis, two distinctive modes of cyclization were revealed to depend on the reaction temperatures. 5<i>H</i>-Benzo­[<i>e</i>]­pyrrolo­[1,2-<i>a</i>]­azepine-1-carbaldehydes with a substituent at the C11 position were obtained as major products at 90 °C as a result of intramolecular 7-<i>endo-dig</i> cyclization, while 6-<i>endo-dig</i> ring closure by electrophilic addition of nitrogen of the pyrrole to a vinyl cation generated under acidic medium followed by an unprecedented domino rearrangement process was observed at 40 °C in some cases, resulting in 5-aryl-11<i>H</i>-benzo­[<i>d</i>]­pyrrolo­[1,2-<i>a</i>]­azepine-1-carbaldehydes along with the former products