The synthesis of selenophene‐fused chromene derivatives starting from 1,3‐diynyl propargyl aryl ethers is reported herein. The method is based on carbon‐carbon, carbon‐selenium, selenium‐carbon and ...carbon‐selenium bonds formation in a one‐pot protocol, using iron(III) chloride and dibutyl diselenide as promoters. The same reaction conditions were applied to propargyl anilines leading to the formation of 1‐(butylselanyl)‐selenophene quinolines. The results showed that the dilution and temperature of substrate addition had a crucial influence in the products obtained. When the substrates were added at room temperature, in the absence of a solvent, a mixture of products was obtained, whereas the slowly addition (15 min) of starting materials, as a dichloromethane solution, at 0 °C led to the product formation in good yields. The mechanistic study indicates that the cooperative action between iron(III) chloride and dibutyl diselenide was essential to promote the cyclization, whereas separately none of them was effective in promoting the cyclization. We proved the synthetic utility of heterocycles obtained in the Suzuki cross coupling reaction, giving the corresponding cross‐coupled products in good yields. In addition, the organoselenium moiety was removed from the structures of products by using n‐butyllithium.
The intramolecular electrophilic cyclization of 3‐organoselanyl‐2‐alkynylindoles providing the synthesis of 3‐iodo‐selenophene‐fused indoles is reported herein. The strategy was extended to the ...preparation of 3‐iodo‐thiophene‐fused indoles in a one‐pot iodine‐promoted thiolation of 2‐alkynylindoles, followed by an electrophilic cyclization sequence. Besides, the synthesis of 3‐butylselanyl‐selenophene‐fused indoles from 3‐butylselanyl‐2‐alkynylindoles was also developed using iron(III) chloride and dibutyl diselenide to promote the cyclization and functionalization of the heterocycle. The identification of the alkyl halide intermediate afforded evidence to the proposed mechanism, which indicated that the reactions proceed through the formation of an iodonium ion, followed by a selenium 5‐endo‐dig cyclization, to afford the indole derivatives. The 3‐iodo‐selenonophene‐fused indoles prepared were applied as substrates in copper‐catalyzed cross‐coupling reactions with thiols to give the Ullmann type products in good yields.
In this paper, we report an intramolecular cyclization of benzylic-substituted propargyl alcohols promoted by iron(III) chloride and diorganyl diselenides to give 2-organoselenyl-naphthalenes via a ...sequential carbon–carbon/carbon–selenium bond formation. The present reaction tolerated a wide range of substituents in both propargyl alcohols and diorganyl diselenides to give the desired 2-organoselenyl-naphthalenes in good yields with high selectivity. In addition, O-acyl protected propargyl alcohol and propargyl bromide were also subjected to this protocol giving the corresponding 2-organoselenyl-naphthalenes. We found that dichalcogenide species affected the formation of cyclized products, whereas diorganyl diselenides gave high yields, moderate yields were obtained with diorganyl disulfides, and no product formation was found with diorganyl ditellurides. The key transformations could be attributed to the carbon–carbon triple bond activation of benzylic-substituted propargyl alcohols by a seleniranium ion, antiattack of the electron cloud from the aromatic ring at the activated triple bond, and cyclization via an exclusive 6-endo-dig process. We also found that the corresponding 2-organoselenyl-naphthalenes are suitable substrates to the selenium–lithium exchange reactions followed by trapping with aldehydes affording the corresponding secondary alcohols.
An iron-catalyzed system, using diorganyl diselenides as an organoselenium source, was used for the cyclization of 1,4-butyne-diols in the preparation of 3,4-bis(organoselanyl)-2,5-dihydrofurans. ...The optimized reaction conditions are compatible with many functional groups in 1,4-butyne-diols and diorganyl diselenides. In addition, this catalyst system was also efficient with diorganyl disulfides, but it did not work for diorganyl ditellurides. The same reaction conditions were also extended to pentyne-1,5-diol for the preparation of 4,5-bis(organoselanyl)-3,6-dihydro-2H-pyrans and to 4-amino-butynol for the preparation of 2,5-dihydro-1H-pyrrole derivatives. The synthetic utility of these heterocycles was studied using 5-bis(organoselanyl)-3,6-dihydro-2H-pyrans as substrate in a Kumada-type cross-coupling reaction.
Iron‐promoted cyclization of 1‐benzyl‐2‐alkynylbenzenes with diorganyl diselenides led to the synthesis of 9‐(organoselanyl)‐5H‐benzo7annulenes whereby the mutual action between diorganyl diselenides ...and iron(III) chloride in a 0.5:1.0 mol ratio was essential in order to achieve the maximal yields of the products. The cyclization reaction tolerated a variety of functional groups, such as trifluoromethyl, chloro, fluoro and methoxy, in both the 1‐benzyl‐2‐alkynylbenzenes and the diorganyl diselenides, giving the seven‐membered heterocyclic products exclusively via a 7‐endo‐dig cyclization process.
We report here the regioselective 6-
-dig cyclization of 2-(butylselanyl)phenylpropynols promoted by the cooperative action between diorganyl diselenides and iron(III) chloride leading to the ...formation of 4-methylene-3-(organoselanyl)-selenochromenes. The results of the reaction condition optimization studies showed that the solvent, the iron source, and the amount of diorganyl diselenide had a fundamental influence on the reaction yields. In the presence of iron(III) chloride (1.5 equiv) and diorganyl diselenides (1.0 equiv), using dichloromethane as the solvent, at room temperature, 4-methylene-3-(organoselanyl)-selenochromenes were formed in moderate to good yields. The reaction conditions were found to be suitable for substrates bearing electron-donating and electron-withdrawing groups on the aromatic ring at both propargyl and alkyne positions. However, we observed a limitation in the reaction conditions when they were applied to other diorganyl dichalcogenides, such as diorganyl disulfides and diorganyl ditellurides, which did not give the corresponding products. We also elaborated on a mechanism proposal based on control experiments performed.
A method for the synthesis of 4‐organoselanyl oxazinoindolone derivatives by the cascade cyclization of N‐(alkoxycarbonyl)‐2‐alkynylindoles using iron(III) chloride and diorganyl diselenides as ...promoters was developed. This protocol was applied to a series of N‐(alkoxycarbonyl)‐2‐alkynylindoles containing different substituents. The reaction conditions also tolerated a variety of diorganyl diselenides having both electron donating and electron withdrawing groups. However, the reaction did not work for diorganyl disulfides and ditellurides. The reaction mechanism seems to proceed via an ionic pathway and the cooperative action between iron(III) chloride and diorganyl diselenides is crucial for successful cyclization. We also found that using the same starting materials, by simply changing the electrophilic source to iodine, led to the formation of 4‐iodo‐oxazinoindolones. The high reactivity of Csp2−Se and Csp2−I bonds were tested under cross‐coupling conditions leading to the preparation of a new class of functionalized indole derivatives. In addition, the absorption, emission and electrochemical properties of 4‐organoselanyl oxazinoindolones showed an important relationship with the substituents of the aromatic rings. The advantages of the methodology include the use of electrophilic to promote the cyclization reaction and functionalization of the indole ring, and the electronic properties presented by the prepared compounds can be exploited as probes, analyte detectors and optical materials.
Synthesis of 4‐organoselanyl oxazinoindolones by the cascade cyclization of N‐(alkoxycarbonyl)‐2‐alkynylindoles using iron(III) chloride and diorganyl diselenides as promoters was developed.
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