Synthesis of pyrone-annulated 2-oxabicyclo[3.3.1]nonanes by palladium-catalyzed cyclization of 4-hydroxy-2-pyrones with allylic bisacetates

Pd-Catalyzed Asymmetric Allylic Substitution Cascade via Desymmetrization for the Construction of Chiral Polyheterocycles

“…[65][66][67] Yoshida et al performed a Pd-catalyzed asymmetric allylic substitution cascade of 4-hydroxy-2Hpyrones (10) with a meso-allyl bisacetate (1h) under reflux conditions and the bridged products 2-oxabicyclo[3.3.1]nonanes rac-11 were formed regioselectively in 65 to 87% yield (►Scheme 9). 68 When the reaction was performed at room temperature, a sole product, the fused-ring tetrahydro-1Hpyrano[4,3-b]benzofuran-1-ones rac-12, could be obtained in 58% yield. However, an efficient synthetic protocol, particularly an asymmetrically catalyzed version of the aforementioned reaction, has not yet been realized.…”

“…7,68,69 First, the treatment of 1e with Pd-complex L 2 Pd 0 forms a π-allylpalladium complex A, which is reacted with nucleophile10 to give the monosubstituted intermediate B. Then, B is converted into π-allylpalladium intermediate C, the key intermediate of the whole reaction, which undergoes two different reaction pathways according to the reaction environment, particularly the reaction temperature.…”