Migratory Decarboxylative Coupling of Coumarins: Synthetic and Mechanistic Aspects

Abstract

Auf Wanderschaft: Die decarboxylierende Kupplung von Allyl‐3‐carboxy‐4‐methylcumarinen liefert die Produkte einer γ‐Allylierung der Methylgruppe – und nicht etwa die der typischen regiospezifischen α‐Allylierung. Mechanistische Studien zeigen, dass ein intramolekularer Protonentransfer von der 4‐Methylgruppe zum 3‐Carboxylat die Allylierung vermittelt und das entstehende 4‐Butenyl‐3‐carboxycumarin dann eine Pd0‐katalysierte Decarboxylierung zu den Produkten eingeht (siehe Schema).

Facile Access to cis‐2,6‐Disubstituted Tetrahydropyrans by Palladium‐Catalyzed Decarboxylative Allylation: Total Syntheses of (±)‐Centrolobine and (+)‐Decytospolides A and B

“…[8] In recent years, however, decarboxylative allylation (DcA) has become a powerful tool for CÀC bond formation and has drawn considerable attention due to its high efficiency, mild reaction conditions, and green features with CO 2 as the only byproduct released. [9] Tunge, [10] Trost, [11] and Stoltz, [12] for instance, have reported a series of catalytic decarboxylative allylation or benzylation reactions. [13] Given the allylic feature of enol ethers (3,4-dihydro-2H-pyran, 1), we envisaged that the use of acetyl acetate as a leaving group could first activate the pyranose system to promote the palladium-induced p-allylation and further decarboxylative coupling would facilitate the CÀC bond formation (Scheme 1c).…”

Recent Advances in the Decarboxylative Strategy of Coumarin‐3‐carboxylic Acid

“…In 2011, Jana and co‐workers reported an exciting example of palladium‐catalyzed migratory decarboxylative allylation of heteroaromatic coumarin substrates 135 (Scheme 31). [52] In this method, instead of the expected allylation at the C‐3 position, it took place at C‐4 position, forming 4‐homoallylcoumarin 136 . Also, Contrary to more often Pd (II) catalyzed decarboxylation reactions, here Pd(0) is catalyzing the decarboxylation process.…”

“…In 2011, Jana and co-workers reported an exciting example of palladium-catalyzed migratory decarboxylative allylation of heteroaromatic coumarin substrates 135 (Scheme 31). [52] In this method, instead of the expected allylation at the C-3 position, it Scheme 29. PIDA/I 2 mediated decarboxylative C-4 amination.…”