Bu3SnH-mediated cyclopropyl radical cyclizations onto indole-3-carbaldehyde

A new era for homolytic aromatic substitution: replacing Bu3SnH with efficient light-induced chain reactions

“…Mechanistic studies have shown that azo-initiator derived radicals [7][8][9][10][11][12] and/or oxygen [12][13][14] may be involved in the hydrogen atom abstraction from the intermediate cyclohexadienyl radical (Scheme 1). It is thus tempting for researchers to add large amounts of azo-initiator however this can result in the incorporation of the initiator derived radicals into the aromatic substitution products [15][16][17] or through radical combination to give non-aromatic products.…”

Tandem Reactions via Barton Esters with Intermolecular Addition and Vinyl Radical Substitution onto Indole

“…13 Most recently, we used Barton esters in radical cyclizations, resulting in some high yielding fiveto seven-membered alkyl and cyclopropyl annulations of indoles and benzimidazoles. 14,15 In the present article, we report a new use of Barton esters, as precursors for one-pot initiator-free cascade/tandem reactions (Scheme 1). The tandem reaction involves intermolecular addition of alkyl radicals onto alkyl propiolates or phenylacetylene, followed by intramolecular substitution of vinyl radicals onto indoles.…”

“…The decomposition of Barton esters { O -acyl thiohydroxamate ester or pyridine-2-thione- N -oxycarbonyl (PTOC)} provides a means of achieving aromatic substitution under mild initiator-free conditions, − as demonstrated by Barton et al for intermolecular substitution of nucleophilic alkyl radicals onto heteroaromatic salts . Most recently, we used Barton esters in radical cyclizations, resulting in some high yielding five- to seven-membered alkyl and cyclopropyl annulations of indoles and benzimidazoles. , In the present article, we report a new use of Barton esters, as precursors for one-pot initiator-free cascade/tandem reactions (Scheme ). The tandem reaction involves intermolecular addition of alkyl radicals onto alkyl propiolates or phenylacetylene, followed by intramolecular substitution of vinyl radicals onto indoles.…”

Cooperative Rh/Chiral Phosphoric Acid Catalysis toward the Highly Stereoselective (3 + 3)-Cycloannulation of Carbonyl Ylides and Indolyl-2-methides

“…As a result, extensive efforts have been directed at the synthesis of azepino­[1,2- a ]­indoles including olefin methathesis, (2 + 5)-cycloaddition, radical cyclization, and transition-metal-catalyzed intramolecular cyclization cascade reactions . Nevertheless, enantioselective approaches are currently underdeveloped, limiting the synthetic access to enantioenriched azepino­[1,2- a ]­indoles …”