Iron‐Promoted Tandem Cyclization of 1,3‐Diynyl Chalcogen Derivatives with Diorganyl Dichalcogenides for the Synthesis of Benzo[b]furan‐Fused Selenophenes

Abstract

Ad ouble intramolecular 5-endo-dig cyclization of butyl[2-(phenylbuta-1,3-diynyl)phenyl]chalcogens has been employed in as electivep reparation of benzo[b]chalcogenopheno[2,3-d]furans. Severalr eactionp arameters were studied to determine the best reactionc onditions and we observed that the reactiono fb utyl[2-(phenylbuta-1,3-diynyl)phenyl]chalcogens (0.25 mmol) with iron(III) chloride hexahydrate (2.0 equiv.) and diorganyl diselenides (1.75 equiv.) at reflux of dichloromethane was the most appropriate to give the productsi n3 5-89% yields.T hese standard reactionc onditions were compatible with many functional groups in the substrates,s uch as methyl, chlorine,f luorine,m ethoxy and heteroaryl. This protocolw as also efficient for diorganyl diselenidesb ut it was ineffective with di-organyl disulfidesa nd ditellurides.I nacompetition among selenium, sulfura nd oxygenn ucleophiles we observed that the nucleophilicity and steric effects of the competingf unctional groups were determinant factorsf or the selectivity of the cyclization. Theb enzo[b]chalcogenopheno[2,3-d]furans had absorptions in the UV region (300-350nmr ange) with molar absorptivity coefficient values ascribed to spin and symmetry allowed p-p*e lectronic transitions.A n emission located in the purple region (380-440nm range), with aS tokes shift of between 65-100 nm, is probably associated to the charge transfer character of the excited state.

Iron(III)‐Promoted Synthesis of 3‐(Organoselanyl)‐1,2‐Dihydroquinolines from Diorganyl Diselenides and N‐Arylpropargylamines by Sequential Carbon‐Carbon and Carbon‐Selenium Bond Formation

“…With regard to the iron source, it was found that FeCl 3 · 6H 2 O was the best iron salt used, leading to the formation of dihydroquinoline 2 a in 76% yield, but a long reaction time was needed ( Table 1, entries [16][17][18][19][20][21]. Further studies revealed that the reaction temperature increase led to a significant decrease in the reaction time, keeping the yield at the same level ( Table 1, entry 22).…”

“…We recently reported that iron salts and diorganyl diselenides are useful alternatives to the cyclization of unsaturated substrates and to introduce organoselenium functionality in heterocycles in a one-step reaction. [21] From a synthetic point of view, the presence of an organoselenium group, directly bonded to Csp 2 becomes the product suitable for further transformations. [22] In addition, the selenium atom can serve as hydrogen-bond acceptor or electron donor, altering the chemical characteristics of enzyme active sites, increasing the native biological activity of the substrate.…”

Insights into the Recent Synthetic Advances of Organoselenium Compounds

“…There have been different strategies for the synthesis of selenated benzofurans or benzothiophenes that creates a path giving more power to drug discovery [49,50] . The pioneering efforts involved the use of commercially unavailable, toxic and unstable RSeCl or diselenides as the selenium source [48,51–58] . Electrophilic cyclizations of 2‐alkynyl phenol derivatives and RSeCl or diselenides were proven to be successful strategies [51–57] .…”

Synthesis of Seleno‐Heterocycles via Electrophilic/Radical Cyclization of Alkyne Containing Heteroatoms

“…[139][140] The reaction of butyl[2-(phenylbuta-1,3-diynyl)phenyl]chalcogen 246 with iron(III) chloride hexahydrate and diorganyl diselenide 4 in dichloromethane solvent under reflux condition resulted in the product benzo[b]chalcogenopheno [2,3-d]furan 247 (Scheme 81). [141] The synthesis of selenophene-fused chromene 249 a and 1-(butylselanyl)-selenophene quinolines derivatives 249 b starting from 1,3-diynyl propargyl aryl ethers and propargyl anilines 248 is shown in Scheme 82. [142] Sonawane et al, reported the synthesis of 1,3-diyne 252 and 1,3,5-triyne 255.…”