An efficient and highly regioselective synthesis of fully substituted furans has been described using Ca(OTf)2. The reaction proceeds through tandem alkylation, 5-exo dig cyclisation and isomerization under solvent free conditions.
Herein we report a facile synthesis of tetracyclic fluorenopyrans from simple acyclic reactants, propargyl alcohols and 3-methylpentane-2,4-dione under calcium catalysis. This one-pot, 3-component reaction proceeds through a sequential allene formation, Friedel-Crafts cyclization/cycloisomerization, intramolecular aldol reaction, Claisen rearrangement, and 6-endo dig cyclization to result in the formation of fluorenopyrans (indeno[2,1-g]chromenes). This strategy was further used in the synthesis of 3-iodofluorenopyrans, by adding iodocyclization to the above sequence of reactions (4-CR). Noticeably, this highly practical, atom and the step-economic procedure is catalyzed by a sustainable (alkaline earth) metal salt and tolerates the broad substrate scope, allowing the further transformations and synthetic utilities of these complex polycyclic moieties.
Highly regioselective synthesis of 3‐Oxindolyl naphthofurans has been described through an interesting Meyer‐Schuster (M−S) type rearrangement followed by oxacyclisation using environmentally benign calcium salt. This synthetic protocol is ornamented with many of the green synthetic aspects such as solvent free, one pot cascade, ‐atom economy, step economy and the use of calcium salt which is highly abundant in the nature. The selected compounds were tested for their preliminary anti‐amyloidogenic properties to highlight the importance of such compounds and methodologies.
6‐(Aryldiazenyl)‐3‐iodoquinolines were prepared from readily available 2‐aminoaryl propargyl alcohols, aryldiazonium salts, and molecular iodine. This three‐component one‐pot process proceeded through sequential azo‐coupling, regioselective iodocyclization, and aromatization reactions to yield the corresponding quinoline derivatives. In the absence of iodine, Ca(OTf)2 was used to promote the azo‐coupling and azacyclization reactions, which furnished the respective 6‐aryldiazenylquinolines. In addition, 2‐aminoaryl propargyl alcohols successfully underwent a regioselective intramolecular cyclization in the presence of Ca(OTf)2 to give 2,4‐disubstituted quinolines. Cross‐coupling reactions of the iodoquinolines were also performed without any effect to the diazo functionality.
A highly facile single‐step synthetic approach to 3‐iodoquinolines has been developed for the first time from readily available 2‐aminobenzophenones and terminal alkynes. The reaction involves the nucleophilic addition of terminal alkynes to 2‐aminobenzophenones followed by a regioselective iodocyclization (6‐endo‐dig) to furnish 2,4‐disubstituted 3‐iodoquinolines in high yields. In general, 2,4‐diaryl‐substituted products were isolated without the need for column chromatography.
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