Deformylative Intramolecular Hydroarylation: Synthesis of Benzo[<i>e</i>]pyrido[1,2‑<i>a</i>]indoles

Attempted cyclization of indolizines bearing both formyl and alkyne groups under acid catalysis provided benzo­[<i>e</i>]­pyrido­[1,2-<i>a</i>]­indoles with an aryl substituent at the C6 position as major products, along with the expected C5-acylated benzo­[<i>e</i>]­pyrido­[1,2-<i>a</i>]­indoles as minor ones, which resulted from preferential deformylative intramolecular hydroarylation instead of intended alkyne-carbonyl metathesis

Total Synthesis of Brazilin

Described herein is a highly efficient total synthesis of brazilin from commercially available starting materials in 9 steps with 70% overall yield. Mitsunobu coupling followed by In­(III)-catalyzed alkyne–aldehyde metathesis allowed for rapid construction of brazilin core skeleton in quantitative yield. Subsequent modulation of oxidation levels and acid-catalyzed cyclization led to the trimethyl ether of brazilin. Asymmetric dihydroxylation of the key intermediate was also demonstrated, which would permit asymmetric access to (+)-brazilin

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

Cycloaromatization Approach to Polysubstituted Indolizines from 2‑Acetylpyrroles: Decoration of the Pyridine Unit

A new synthetic route to indolizines with various substituents on the pyridine moiety was developed by utilizing a facile cycloaromatization of 2-acetylpyrrole derivatives. Without isolation, the resulting intermediates were allowed to react with various electrophiles to afford a range of indolizines. In particular, Suzuki–Miyaura cross-coupling of <i>O</i>-triflates with (hetero)­arylboronic acids permitted introduction of diverse substituents at the C8 position of an indolizine skeleton

Skeletal Reorganization: Synthesis of Diptoindonesin G from Pauciflorol F

Described herein is a novel synthetic approach to diptoindonesin G, a highly potent anticancer oligostilbenoid natural product, from pauciflorol F pentamethyl ether through a skeletal reorganization strategy where oxidative cleavage of the indanone ring system of pauciflorol F and sequential cyclization of the key intermediate allowed direct access to the target skeleton

Skeletal Reorganization: Synthesis of Diptoindonesin G from Pauciflorol F

Described herein is a novel synthetic approach to diptoindonesin G, a highly potent anticancer oligostilbenoid natural product, from pauciflorol F pentamethyl ether through a skeletal reorganization strategy where oxidative cleavage of the indanone ring system of pauciflorol F and sequential cyclization of the key intermediate allowed direct access to the target skeleton

Domino Knoevenagel Condensation/Intramolecular Aldol Cyclization Route to Diverse Indolizines with Densely Functionalized Pyridine Units

A highly efficient [4 + 2] annulation route to polysubstituted indolizines is described employing a domino Knoevenagel condensation/intramolecular aldol cyclization process as a key step. Construction of pyridine rings in indolizine skeleton was rapidly achieved from several pyrrole-2-carboxaldehydes in good to excellent yields, leading to indolizines with various substituents at the 5, 6, and 7 positions depending on the reacting active methylene partners

Palladium-Catalyzed α‑Arylation of Aryloxyketones for the Synthesis of 2,3-Disubstituted Benzofurans

A highly efficient palladium-catalyzed α-arylation of aryloxyketones has been developed, allowing for facile installation of various (hetero)­aryl groups at C2 position in good to excellent yields. Subsequent cyclodehydration of the resulting α-arylated aryloxyketones provided rapid access to diverse 2,3-disubstitured benzofurans

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