Palladium-catalyzed decarboxylation [2 + 2 + 2] annulation approach to chromone-containing polycyclic compounds

Abstract

A variety of chromone-containing polycyclic compounds are efficiently generated via Pd-catalyzed decarboxylation [2 + 2 + 2] annulation of 3-iodochromones, bridged olefins and o-bromobenzoic acids, in which o-bromobenzoic acids were employed as the electrophilic aryl units.

Iodomethane in C1 chemistry: application in palladium-catalyzed [2 + 2 + 1] annulation

“…In our previous investigations, chromonyl-norbornyl-palladacycle (CNP) generated from 3-iodochromone, norbornene(NBE), and a Pd(0) catalyst has been proved to be an active Pd( ii ) species, which could further react with some electrophilic reagents, including α-bromoacetophenones, 6 benzyl bromides, 7 cyclopropenones, 8 aziridines 9 and o -bromobenzoic acids, 10 affording different kinds of chromone-incorporated derivatives via palladium-catalyzed [2 + 3 + 1], [2 + 2 + 1] and [2 + 2 + 2] domino annulations (Scheme 1A). 11…”

“…Based on our previous work 6–10,12 and related literature 11,16 on the palladium-catalyzed reaction involving palladacycle intermediates, a plausible mechanism is proposed in Scheme 6. Firstly, Pd(0) species were generated in situ from Pd(OAc) 2 .…”

Toward the Generation of 2-Amino-3-Formyl Difunctionalized Chromones via Pd-Enabled Rearrangement Strategy

“…Hence, exploration of a novel strategy toward the syntheses of chromone derivatives, especially the multifunctionalized chromones, is highly desirable. Considering the character of ring-opening of isoflavones to form the phenoxy anion under basic conditions (Figure e) and the unique properties of isocyanides in organic synthesis as well as our continuous interest in the elaboration of chromonyl-norbornyl-palladacycle intermediate for the construction of various chromone derivatives, − we wondered if the phenoxy anion intermediate could be engaged in a ring-closure reaction under palladium-catalyzed conditions, delivering the functionalized chromones, rather than undergoing a competitive decarboxylation event, thus generating the undesired ketone byproduct. Herein, we report our most recent endeavor on the molecular rearrangement of 3-halogenochromones based on functional group transformation; this protocol provides a seemingly direct ortho -C–H amination and ipso -formylation of 3-halogenochromones with isocyanides enabled by palladium catalysis under basic conditions (Figure f).…”