Cobalt(III)-Catalyzed Chemo- and Regioselective [4 + 2]-Annulation of Aromatic Sulfoxonium Ylides with 1,3-Diynes

Abstract

Air-stable, highly abundant, and cost-effective Co(III)-catalyzed redox-neutral [4 + 2]-annulation of aromatic sulfoxonium ylides with 1,3-diynes providing useful substituted 1-naphthol derivatives in a regioselective manner is described. Further, the prepared 1-naphthols having internal alkyne were converted into useful polycarbocyclic molecules and spiro-dienone derivatives in good-to-excellent yields. A possible reaction mechanism involving ortho C−H activation as a key step was proposed and supported by deuterium labeling and kinetic isotope labeling studies.

Cobalt(III)-Catalyzed Regioselective [4 + 2]-Annulation of N-Chlorobenzamides with Substituted Alkenes

“…Typically, Pd, Rh, Ru, and Ir metal complexes are widely used as a catalyst in this type of annulation reaction. , In recent years, there has been a tremendous approach toward more accessible 3d metals such as Co, Cu, Fe, Mn, and Ni as a catalyst in C–H functionalization reactions. − Furthermore, most of these transformations demand the utility of stoichiometric amounts of external oxidants to regenerate the active catalyst. It is worth mentioning that for these types of annulation reactions, exogenous oxidants can be avoided by employing or introducing the internal oxidant (N–N, N–O, N–S, O–N, and O–O bonds) containing directing groups . During this transformation, the oxidizing directing group internally oxidizes the metal to replenish the active catalyst and avoids undesired product formation in a redox-neutral manner.…”

Regioselective Dichotomy in Ru(II)-Catalyzed C–H Annulation of Aryl Pyrazolidinones with 1,3-Diynes

“…In 2014, Glorius and co-workers in a pioneering report illustrated Rh­(III)-catalyzed synthesis of 3-alkynylated isoquinolones employing 1,3-diynes . Later, different research groups including us unveiled several methods to couple 1,3-diynes with various directing groups in the presence of transition metals like Rh­(III), Co­(III), and Ru­(II) . The main challenge associated with the use of 1,3-diynes is the ambiguity related to regioselectivity during the migratory insertion with an organometallic intermediate (Scheme a).…”

Synthesis of Indenone Derivatives by Rh(III)-Catalyzed C–H Functionalization of Sulfoxonium Ylides with 1,3-Diynes

“…In this scenario, several traceless DGs are well studied; among them, sulfoxonium ylide has a significant impact because of its high flexibility and diversity of participation in various annulations such as [4 + 2], [4 + 1], and [3 + 3] . In particular, the use of an alkyne moiety with sulfoxonium ylides in transition-metal-catalyzed C–H functionalization would enable the rapid assembly of naphthol derivatives (Scheme a) . Similarly, sulfoxonium surrogates such as phosphonium ylides and enaminones were also effectively coupled with alkynes to furnish the naphthol moieties .…”

“…The tautomerization of intermediate D produces intermediate E . In the general pathway, intermediate E follows carbenoid formation via α-elimination of DMSO/Rh–alkenyl bond insertion/protodemetalation to furnish the [4 + 2]-annulation product . In contrast, here the HFIP solvent alters the catalytic pathway with the help of AcOH .…”