Mild, Modular, and Convergent Synthesis of Helical Naphtho[2,1-c]chromenes via a Multistep Cyclization/Aromatization Cascade Sequence

Tetracyclic 6H-naphtho[2,1-c]chromenes are expeditiously synthesized through a BF₃·OEt₂-mediated, three-step cascade reaction, creating new central pyran and aromatic rings. The cascade involves the addition of phenol-derived alkynyl substrates to BF₃-activated aldehydes followed by alkyne-Prins cyclization, Friedel-Crafts reaction, and final elimination. Aliphatic and electron-deficient aromatic aldehydes afford the products in 50-74% isolated yields, but benzaldehyde and tolualdehyde resulted in lower yields. X-ray analysis of a p-bromophenyl derivative (5aA) shows the two aromatic moieties are twisted by 28° to create a helical backbone.

Regiospecific alkyl addition of (hetero)arene-fused thiophenes enabled by a visible-light-mediated photocatalytic desulfuration approach

A unique photoredox desulfuration approach enabling the regiospecific alkyl addition of (hetero)arene-fused thiophenes is presented.

Electronic effects on a one-pot aromatization cascade involving alkynyl-Prins cyclization, Friedel–Crafts alkylation and dehydration to tricyclic benzo[f]isochromenes

A short, efficient cyclization/aromatization cascade affords tricyclic 1,4-dihydro-2H-benzo[f]isochromenes. Electronic factors suggest concerted alkynyl-Prins and Friedel–Crafts reactions in the sequence.

Stereoselective synthesis of thiazino[4,3-a]indoles using the thia-Pictet-Spengler reaction of indoles bearing N-tethered thiols and vinylogous thiocarbonates

An inter- as well as intra-molecular thia-Pictet-Spengler cyclization of N-tethered thiols and vinylogous thiocarbonates is described for the stereoselective synthesis of N-fused thiazinoindole derivatives. The strategy is extended to one-pot, sequential Friedel-Crafts alkylation - Pictet-Spengler cyclization and the synthesis of thiazino-oxepino-indole.

Synthesis of benzofurans via an acid catalysed transacetalisation/Fries-type O → C rearrangement/Michael addition/ring-opening aromatisation cascade of β-pyrones

An unusual and facile approach for the synthesis of 2-benzofuranyl-3-hydroxyacetones from 6-acetoxy-β-pyrones and phenols is presented.

Stereoselective synthesis of 2,3-disubstituted indoline, pyrrolidine and cyclic ether-fused 1,2-dihydroquinoline derivatives using alkyne iminium ion cyclization of vinylogous carbamates: switch of regioselectivity using an internal hydroxy group as a nucleophile

TMSOTf promoted alkyne iminium ion cyclization of vinylogous carbamates gives stereoselective access to indolines, pyrrolidines and dihydroquinolines.