Unexpected ortho-Heck Reaction under the Catellani Conditions

Tunable Construction of Multisubstituted 1,3-Dienes and Allenes via a 1,4-Palladium Migration/Carbene Insertion Cascade

Efficient palladium-catalyzed vinylic C-H alkenylation and allenylation of gem-disubstituted ethylenes with N-tosylhydrazones of aryl alkyl and diaryl ketones were achieved to access trisubstituted 1,3-dienes and tetrasubstituted allenes, respectively. An aryl to vinyl 1,4-palladium migration/carbene insertion/β-hydride elimination sequence proceeded to switch the chemo- and regioselectivities to give structurally diverse products. Use of 2-FC₆H₄OH additive enables enhancement of the reaction efficiency through accelerating the key 1,4-palladium migration process.

Tandem Reactions involving 1,4-Palladium Migrations

Transition-metal-catalyzed tandem reactions have become a mainstay in organic chemistry owing to their high atom- and step-economies. Metal-migration-based tandem reactions allow the engagement of simple starting materials for incorporating functional groups into certain positions and constructing complex scaffolds, which provide novel means that are complementary to traditional cross-coupling or C-H activation processes. In light of the broad utility of the 1,4-Pd migration reaction, this paper reviews its progress in the past two decades, summarizing the tandem process and classifying it based on insertion, elimination, transmetalation, and C-H bond activation. Special emphasis is placed on the driving force of Pd migration and different migration mechanisms. Moreover, this review also attempts to summarize common strategies for improving the regio- and site-selectivities of the migration process.

Redox-Neutral Vicinal Difunctionalization of Five-Membered Heteroarenes with Dual Electrophiles

A new reaction mode of palladium/norbornene (Pd/NBE) cooperative catalysis is reported involving the selective coupling of two different carbon-based electrophiles for vicinal double C-H functionalization of five-membered heteroarenes in a site-selective and redox-neutral manner. The key is to use alkynyl bromides as the second electrophile, which allows vicinal difunctionalization of a wide range of heteroarenes including pyrroles, thiophenes and furans at their C4 and C5 positions. One- or two-step tetrafunctionalizations of simple pyrrole and thiophene have also been realized. The C2-substituted NBEs prove most effective in these reactions, and the mechanistic exploration discloses the origin of the high selectivity of this transformation. Synthetic utility of this method has been exemplified in the concise preparations of thiophene-containing organic materials and a protein kinase inhibitor analogue. Preliminary success has also been achieved in a direct annulation event, using a tethered ketone as the second electrophile.

Intermolecular C-H silylation through cascade carbopalladation and vinylic to aryl 1,4-palladium migration

A palladium-catalyzed remote C-H silylation reaction has been developed through vinylic to aryl 1,4-palladium migration. By using alkyne-tethered aryl iodides as the starting materials and hexamethyldisilane as the silylating reagent, the reaction involves cascade intramolecular carbopalladation, 1,4-palladium migration, and silylation with hexamethyldisilane, and leads to the formation of exocyclic alkene-containing 5-silylisoquinolines as the final products.

Pd/NBE-catalyzed sequential carbamoylation/olefination of aryl iodides

We present a Pd/NBE-catalyzed sequential carbamoylation/olefination of aryl iodides under mild reaction conditions, which provide diverse 4-methylene-3,4-dihydro-1(2H)-isoquinolin-1-one analogues.

Recent advances in transition metal migration involving reactions

In this review, various types of metal-migration involved methodologies, including palladium, rhodium, iron, cobalt, iridium, chromium, nickel, platinum, are summarized and demonstrated elaborately for giving a better access to this field.