Intramolecular cyclization of nitrogen tethered alkenols catalyzed by palladium chloride leads to substituted morpholines in good yields. The methodology was used for the total synthesis of (±)-chelonin A.
Intramolecular hydroalkoxylation/hydrothioalkoxylation of nitrogen-tethered alkenes and alcohols/thiols mediated by boron trifluoride etherate leads to five-membered thiazolidine, six-membered 1,4-oxazines (morpholines) and tetrahydro-2H-1,4-thiazines (thiomorpholines), and seven-membered 1,4-oxazepanes in good yields.
Nano-S prepared by an annealing process showed excellent catalytic activity for the synthesis of 1-amidoalkyl-2-naphthols under solvent-free reaction condition at 50 °C. The catalyst could be reused up to the fifth cycle without loss in its action. The green-ness of the present protocol was also measured using green metrics drawing its superiority.
A convenient protocol has been established for the synthesis of 1-tosyl-2,3,4,5-tetrahydro-1H-indeno[1,2-b]pyridine via cascade cyclization and Friedel-Crafts reaction of 4-methyl-N-(pent-4-yn-1-yl)benzenesulfonamides and aldehydes in good yields. The methodology has been used for the total synthesis of the antidepressant agent (±)-5-phenyl-2,3,4,4a,5,9b-hexahydro-1H-indeno[1,2-b]pyridine.
Bismuth trifluoromethanesulfonate can be efficiently used for the preparation of dihydropyrans from βallenols and aldehydes by oxonium−ene reaction in good yields. The reaction is highly regioselective. On the other hand, the same reaction with trimethylsilyl trifluoromethanesulfonate at −45 °C affords the hexahydropyrano[4,3-b]pyran skeleton in moderate yields.
Tetrahydrothiophenes and -thiopyrans have been efficiently synthesized from thioacrylates via thia-Prins cyclization reaction mediated by trimethylsilyltrifluoromethanesulfonate with good diastereoselectivity and in good to high yields.
Dihydroindeno[1,2-c]isochromene can be efficiently prepared from alkynol and aldehydes via cascade cyclization and Friedel–Crafts reaction. The reaction is highly regioselective.
An intramolecular carbenium ion induced cyclization of N‐tethered alkyne‐benzyl alkanols mediated by ferric chloride (FeCl3) leading to substituted pyrrolidines and piperidines with exocyclic chloro‐alkylidene and ‐arylidene moiety in good yields has been described. The reaction proceeds in an anti‐fashion in both the cases. Ferric chloride acts both as Lewis acid as well as chloride nucleophile.
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