Dodging the Conventional Reactivity of o-Alkynylanilines under Gold Catalysis for Distal 7-endo-dig Cyclization.

A direct ring-closing strategy involving a less facile 7-endo-dig carbacyclization of o-alkynylaniline derivatives for the synthesis of benzo[b]azepines has been presented. The trivial well-documented 5-endo-dig cyclization in o-alkynylaniline derivatives due to high nucleophilicity of nitrogen has been overcome by using their vinylogous amides under gold catalysis to access a wide array of benzo[b]azepines in an atom economical way with excellent functional group compatibility. Deuterium scrambling experiments and DFT studies favor a mechanism involving stabilizing conformational change of the initially formed seven-membered vinyl gold intermediate through a key cyclopropyl gold carbene intermediate and its subsequent protodeauration mediated by the counter anion.

TfOH-promoted synthesis of indoles and benzofurans involving cyclative transposition of vinyl ketone.

A metal-free approach to construct indole rings from vinylogous amides derived from o-alkynylanilines involving a cyclization, retro-aza-Michael reaction and amine trapping cascade is reported here. This atom-economical transformation has been extended to synthesize benzofuran derivatives using analogous vinylogous esters derived from o-alkynylphenols. The excellent stereochemical outcome of the double bond geometry in the products makes it attractive.

Brønsted/Lewis Acid-Promoted Site-Selective Intramolecular Cycloisomerizations of Aryl-Fused 1,6-Diyn-3-ones for Diversity-Oriented Synthesis of Benzo-Fused Fluorenes and Fluorenones and Naphthyl Ketones.

Herein, a facile diversity-oriented approach to access functionalized benzo[a]fluorenes, benzo[b]fluorenones, and naphthyl ketones has been demonstrated via site-selective intramolecular cyclization of aryl-fused 1,6-diyn-3-ones. Synthesis of benzo[a]fluorenes and naphthyl ketones has been achieved selectively using TfOH and AgBF4, respectively, via in situ-formed acetals. Aryl-fused 1,6-diyn-3-ones undergo triflic acid-mediated intramolecular cyclization, leading to benzo[b]fluorenone derivatives via a radical intermediate as supported by EPR studies. Kinetic studies of these transformations have also been performed by UV-visible spectroscopic analysis to shed light on the reaction profile.