Migratory Decarboxylative Coupling of Coumarins: Synthetic and Mechanistic Aspects

Abstract

On the move: Decarboxylative coupling of allyl 4‐methyl‐3‐carboxycoumarins provides the products of γ‐allylation of the methyl group rather than the typical regiospecific α‐allylation. Mechanistic studies show that intramolecular proton transfer from the 4‐methyl group to the 3‐carboxylate allows allylation of the remote methyl group. The resulting 4‐butenyl‐3‐carboxyl coumarin undergoes Pd0‐catalyzed decarboxylation to provide the observed products (see scheme).

Exploiting Distal Reactivity of Coumarins: A Rhodium‐Catalyzed Vinylogous Asymmetric Ring‐Opening Reaction

“…In general, this protocol tolerates awide spectrum of substrates with varying electronic and steric properties.S ymmetric oxabicyclic alkenes bearing electron-donating groups (3c, 3e, 3h, 3m,and 3n)and electron-withdrawing groups (3b, 3d, 3f, 3i, 3j,a nd 3l)p roceeded smoothly in this reaction to generate the corresponding ring-opened products (3). While previous reports noted that similar substrates failed to react in palladium-catalyzed allylation reactions, [4] our protocol accommodates the g-branched 1g to generate an 80 %combined yield of two diastereomers (1.1:1 d.r. Generally,yields ranged from good to excellent and enantioselectivities were almost always excellent.…”

“…[4] Subsequently,H artwig and co-workers established the first asymmetric iridium-catalyzed g-allylation utilizing adioxinone-derived silyl-enol dienolate in 2014. One area that has gained significant momentum is the transition metal catalyzed g-allylation reaction (Scheme 1).…”

“…In 2011, Tu nge and coworkers reported their seminal studies in the palladiumcatalyzed migratory decarboxylative g-allylation of coumarins. [4] Subsequently,H artwig and co-workers established the first asymmetric iridium-catalyzed g-allylation utilizing adioxinone-derived silyl-enol dienolate in 2014. [5] Very recently, Jørgenson and co-workers disclosed asynergistic approach by combining chiral amine organocatalysis and iridium catalysis to effect g-allylation of a,b-unsaturated aldehydes.…”

Ligand‐Controlled Regiodivergent Palladium‐Catalyzed Decarboxylative Allylation Reaction to Access α,α‐Difluoroketones

“…[1] Moreover, this strategy enables the formation of reactive intermediates and regioselective coupling to provide products that might be difficult to access otherwise. [2] While Pd-catalyzed decarboxylative allylation reactions of soft C-based (e.g. malonates, β -diketones, β -ketoestsers) and heteroatom-based nucleophiles can provide both branched [3] and linear [4] products, Pd-catalyzed allylation reactions of hard enolate-nucleophiles with monosubstituted allylic substrates almost exclusively provide linear products.…”

Palladium-catalyzed, pyrrolidine-mediated arylmethylation of ketones and aldehydes with coumarinyl(methyl) acetates

“…15 For this reason, our group has continued to develop “milder” reaction conditions for the coupling of nucleophiles to coumarin moieties. 16 Current literature protocols for the electrophilic introduction of 4-methyl-2 H -chromen-2-one involved displacement of halides from the 4-methyl substituent. 14,17 To date, there is only a single report for the addition of a ketone nucleophile to an electrophilic Pd-π-benzyl complex generated from the ionization of 4-methyl-coumarin esters (eqn (5), I).…”