Synthesis of α-pyrones via gold-catalyzed cycloisomerization/[2 + 1] cycloaddition/rearrangement of enyne-amides and sulfur ylides

Abstract

A novel gold-catalyzed cycloisomerization/[2 + 1]cycloaddition/rearrangement of enyne-amides and sulfur ylides is reported. This strategy enables rapid and efficient construction of a series of α-pyrone derivatives.

Highly Diastereoselective One-Pot Synthesis of 4,5-Dihydrofuro[2,3-b]azocin-6-one Derivatives through Cyclization/[4+4] Annulation Reactions

“…The efficient assembly of the furo-azocinone derivatives from easily accessible starting materials still remains to be further explored. On the other hand, dihydrofuran-fused azadienes could be constructed through the transition metal-catalyzed 5-endo-dig annulation of enyne-amides , that are a class of derivatives of enyne-ones . Because of their preexisting s -cis conformation, aromatization-driven force, and polar conjugated system, these in situ generated azadienes have been designed as powerful 4-atom synthons for the efficient synthesis of furan-fused heterocyclic molecules through [4+ n ] annulation. , For example, a series of bicyclic lactams were highly efficiently and enantioselectively generated via the gold and NHC co-catalyzed cyclization/[4+2] annulation between enyne-amides and enals .…”

“…On the other hand, dihydrofuran-fused azadienes could be constructed through the transition metal-catalyzed 5-endo-dig annulation of enyne-amides , that are a class of derivatives of enyne-ones . Because of their preexisting s -cis conformation, aromatization-driven force, and polar conjugated system, these in situ generated azadienes have been designed as powerful 4-atom synthons for the efficient synthesis of furan-fused heterocyclic molecules through [4+ n ] annulation. , For example, a series of bicyclic lactams were highly efficiently and enantioselectively generated via the gold and NHC co-catalyzed cyclization/[4+2] annulation between enyne-amides and enals . The Zhao group reported the domino synthesis of furan-fused nine-membered heterocycles through the enantioselective [5+4] cycloaddition of the in situ formed azadienes with vinylethylene carbonates under Au/Pd sequential catalysis .…”

“…In order to overcome the shortcomings of previous access to furan-fused azocine derivatives, and continue our efforts to exploring new one-pot strategies for the elaboration of heterocycles, , we designed a novel one-pot synthesis of furo­[2,3- b ]­azocin-6-one derivatives through a cyclization/[4+4] annulation reaction of enyne-amides and ynones (Scheme ). There are several challenges for this new transformation, including the control of the stereochemistry, the regioselectivity of the annulation (formation of 3 vs I ), and the selective [4+4] annulation instead of [4+2] cycloaddition (formation of 3 vs II/III ) …”

Selective Fluorosulfonylation of Thianthrenium Salts Enabled by Electrochemistry

“…On the contrary, by employing the good site-selective prethianthrenation of aromatic C–H bonds, pioneered by the groups of Ritter and Wang, a variety of elegant coupling reactions have recently been developed . Although these protocols show excellent applications, they mainly rely on the use of transition metal catalysis or photoredox catalysis to activate thianthrenium salts (Figure B). − Broadening the synthetic applicability with the new activation model remains underdeveloped . In this context, considering that the reductive potential of stable and easy-to-handle aryl thianthrenium salts (TT) is around −1.5 V (vs SCE) and driven by the intrinsic advantage of electrosynthesis using electron as a green redox reagent to activate substrates under mild reaction conditions, we envisioned that thianthrenium salts should be facilely reduced to form the carbon-based radicals at the cathode under a suitable voltage, based on our previous works .…”

Highly efficient construction of 2,3-disubstituted indoline derivatives by [4 + 1] annulation of sulfur ylides and o-sulfonamido aldimines

“…8 The research groups of Aggarwal, 9 Tang, 10 Xiao, 11 Huang 12 and others 13 have disclosed many elegant reactions of sulfur ylides used to generate novel compounds. As part of our ongoing research program on methods to synthesize carbo- and hetero-cycles, 14 we report an efficient synthesis of 2,3-disubstituted indolines that relies on metal-free [4 + 1] cycloaddition of sulfur ylides and o -sulfonamido aldimine (Fig. 1C).…”