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.
This paper describes an alternative method for the synthesis of 3‐organoselanylbenzo[b]furans through the intramolecular cyclization of 2‐alkynylphenols promoted by copper iodide and diorganyl diselenides. The cyclization reactions were carried out at room temperature in the absence of base and under air (open flask). This synthetic approach proved to be efficient with both diorganyl diselenides and 2‐alkynylphenols bearing electron‐neutral, electron‐donating, and electron‐withdrawing substituents. 2‐Phenyl‐3‐phenylselanylbenzo[b]furan was used as a synthetic precursor in organochalcogen–lithium exchange and bromination reactions, allowing the synthesis of functionalized benzo[b]furans in good yields.
A synthetic approach to regioselective synthesis of 3-organochalcogenyl spiro[4,5]trienones and 3-organochalcogenyl[4,5]triene-2,6-diones is described through the reaction of arylpropiolamides with an electrophilic chalcogen source.
We describe here the Lewis acid‐promoted cyclization reaction of benzomidazole thiols with propargyl alcohols for the selective synthesis of benzoimidazolo thiazines and benzothiazolo imidazoles. The reaction is regioselective and the solvent controls the formation of products. The systematic study to determine the best reaction conditions revealed that the six‐membered benzoimidazolo thiazines were obtained by reacting the benzoimidazole thiols with propargyl alcohols in the presence of boron trifluoride etherate, using dichloromethane as the solvent. Replacement of dichloromethane with dimethylformamide, by using the same starting material and reagents, gave selectively the five‐membered benzothiazolo imidazoles. The mechanism of this cyclization was proposed based on the results obtained and several control experiments.
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