Thiol mediated 8-endo-trig radical cyclization: an easy access to medium-sized cyclic ethers

An efficient new method for the synthesis of eight-membered heterocycles has been developed via a thiophenol mediated intramolecular 8-endo radical cyclization reaction. Alkenyl radicals are generated from easily available terminal alkynes and thiophenol.     

Thiophenol-mediated intramolecular radical cyclization: an efficient method for the synthesis of benzoxocine derivatives

A new, efficient, high yielding method for the synthesis of benzoxocine derivatives has been developed via a thiophenol-mediated intramolecular 8-endo radical cyclization. This method allowed the synthesis of the backbone of several sesquiterpenes.     

Thiophenol-catalyzed Claisen rearrangement and radical cyclization: formation of furo- and pyrano-coumarin derivatives

Regioselective synthesis of dihydrofurocoumarins and dihydropyranocoumarins in excellent yields from 4-prop-2-ynyloxy coumarin via a thiol mediated radical reaction is described. Alkenyl radicals are generated from easily available terminal alkynes and thiophenol. Thiophenol catalyzed the Claisen rearrangement of the 4-prop-2-ynyloxycoumarin ethers.     

Convenient switching of 7-endo/6-exo radical cyclization

7-endo/6-exo Selectivity of radical cyclization to α,β-unsaturated amides was readily controlled by the presence or absence of a temporary substituent, a phenylthio or chlorine group, at the α-position of the acceptor.     

An easy access to pyrimidine-fused azocine derivatives by thiophenol-mediated radical cyclization via 8-endo-trig mode

An efficient route for the synthesis of eight-membered nitrogen heterocycles has been developed via a thiophenol-mediated intramolecular 8-endo-trig radical cyclization. The radical precursors were prepared using BF₃·Et₂O-catalyzed aza-Claisen rearrangement followed by the reaction with propargyl bromide. The alkenyl radicals are generated from thiophenol initiated by the benzoyl peroxide instead of commonly used AIBN for easy and facile isolation of the pure products.     

Regioselective synthesis of quinolone-annulated sulfur heterocycles by aryl radical cyclization

The tin hydride-mediated cyclizations of a number of sulfides and sulfones under mild, neutral conditions, have been investigated accompanied by some amount of β-scission product for sulfides. The sulfides were derived from 4-mercaptoquinolone and 2-bromobenzyl bromides by phase transfer catalyzed reaction and the corresponding sulfones were prepared by treatment of the sulfides with m-CPBA at room temperature. The sulfides and the corresponding sulfones were then reacted with ⁿBu₃SnH-AIBN to give regioselective quinolone-annulated sulfur heterocycles.     

Thiophenol mediated radical cyclization: an expedient approach to 2H-pyrrolo[3,2-d]pyrimidines (9-deazaxanthine analogs)

A new efficient route for the synthesis of substituted 2H-pyrrolopyrimidines (9-deazaxanthine analogs) via thiophenol mediated radical cyclization has been achieved. The stereochemistry of the newly synthesised compounds has been settled from NOE data.     

A tandem radical cyclization approach to 3-(2-oxopyrrolidin-3-yl)indolin-2-ones, potential intermediates toward complex indole-heterocycles

A series of substituted 3-(2-oxopyrrolidin-3-yl)indolin-2-one derivatives have been synthesized by tris(trimethylsilyl)silane (TTMSS) induced tandem radical cyclization as key step.     

Palladium-catalyzed tandem cyclization of fluorinated imidoyl chlorides with 2-bromophenylboronic acid: Synthesis of 6-fluoroalkyl-phenanthridines

An efficient method has been developed to synthesize 6-fluoroalkyl-phenanthridines via the palladium-catalyzed tandem cyclization of fluorinated imidoyl chlorides with 2-bromophenylboronic acid. This methodology facilitates the rapid synthesis of 6-fluoroalkyl-phenanthridines through dual C–C bond formation in an oxidant-free one-pot manner.     

Topologically driven tandem radical cyclization-based strategy for the synthesis of oxa- and aza-cages

Tandem radical cyclization-based strategy for the synthesis of oxa- and aza-cage compounds is described. The aryl iodides 1 and N-tosyl propargylated amine 8 lead to oxa- and aza-cages, respectively, after two tandem 5-exo-trig radical cyclizations. The alcohols 11 on reaction with ⁿBu₃SnH and AIBN give rise to the oxa-cages 14 bearing the tributyltin moiety after three tandem 5-exo-trig cyclizations. On the other hand, reaction of the propargyl ether 16 under similar conditions furnishes the oxa-cage 17 by a 5-exo-trig, 4-exo-trig, 5-exo-trig tandem radical cyclization sequence.     

The stereoselective synthesis of tetrahydrothiopyrano[2,3-b]indole skeletons via tandem reaction of indoline-2-thiones to Baylis–Hillman adduct acetates

Indoline-2-thiones (5) were applied as 1,3-dinucleophiles in a tandem reaction with Baylis–Hillman adduct acetates (4) to give novel tetrahydrothiopyrano[2,3-b]indole skeletons (6). The effect of different solvents, bases, and catalysts on the yields and stereochemical outcome was studied in detail. The results indicated that acetonitrile as solvent and K₂CO₃ as base, under reflux conditions, were the optimum conditions. Products 6a–6l were obtained in high diastereoselectivity and yield (up to 94%).     

PTSA-catalyzed tandem cyclization protocol for the stereoselective total synthesis of obolactone

Stereoselective total synthesis of obolactone by the Brønsted acid (PTSA) mediated tandem cyclization of the appropriately substituted diketone in one-pot in a highly selective and efficient manner is reported.     

通过自由基加成环化反应制备香豆素衍生物的研究进展

香豆素衍生物是一类重要的杂环内酯化合物,广泛应用于有机合成、生物医药及荧光材料等领域。开发新型简单高效的功能化香豆素合成策略一直受到人们的关注,通过苯丙炔酸酯与各类自由基前驱体的直接自由基加成环化反应为香豆素衍生物的功能化修饰提供了一条简单、清洁、高效的合成路线。本文综述了近年来基于自由基加成环化历程制备各类功能化香豆素衍生物的新进展。     

One-pot synthesis of [1,2,4]Triazolo[1,5-a]pyridines from azines and benzylidenemalononitriles via copper-catalyzed tandem cyclization

A simple and efficient copper-catalyzed tandem radical cyclization reaction has been discovered for the synthesis of triaryl [1,2,4]triazolo[1,5-a]pyridines from easily accessible azines and benzylidenmalononitriles. The new transformation involves multiple CH/CC bonds cleavage and CC/CN bonds formation, with extrusion of gaseous hydrogen and methane. A wide variety of substrates with different functional groups could be converted into the corresponding products in good yields. The fused heterocycles have strong blue fluorescence with large Strokes shifts and high quantum yields.     

Efficient synthesis of aryl-substituted carbazoles via tandem double or triple suzuki coupling and cadogan cyclization

An efficient one-step method to prepare aryl-substituted carbazoles via tandem double or triple CC bond formations by multiple Suzuki couplings and CN bond formation by Cadogan cyclization has been developed. The developed method employs commercially available or easily preparable polybromonitrobenzenes and arylboronic acids as starting materials, tolerates various functional groups, and provides good yields.     

Palladium-mediated reductive Mizoroki-Heck cyclization strategy for the regioselective formation of dibenzoazocinone framework

The synthesis of dibenzoazocine framework through palladium-mediated reductive Mizoroki-Heck cyclization has been described. The procedure is simple, straightforward, and regioselective.     

Stereoselective tandem synthesis of oxazolo-fused pyrroloquinolines from o-alkynylaldehydes via Ag(I)-catalyzed regioselective 5-exo-dig ring closure

A tandem approach for the regio- and stereoselective synthesis of oxazolo-fused pyrroloquinolines 3a–l via the reaction of o-alkynylaldehydes 1a–i with chiral amino alcohols 2a–c under mild reaction conditions is described. The possible participation of the pyridine ring in the regioselective formation of 5-exo-dig cyclized products was supported by the controlled experiments. The structures and stereochemistry of the products were confirmed by NOESY and X-ray crystallographic studies.     

Domino-Knoevenagel-hetero-Diels-Alder reactions: an efficient one-step synthesis of indole-annulated thiopyranobenzopyran derivatives

Rapid one-step synthesis of hitherto unreported indole-annulated pentacyclic heterocycles containing oxygen, nitrogen, and sulfur has been described by domino-Knoevenagel-hetero-Diels-Alder reaction. The reaction sequence provides a route to the synthesis of a novel type of polyheterocycles in excellent yields with high stereoselectivity.