Progress of Catalytic Asymmetric Diels-Alder Reactions of 2-Pyrones

Synthesis of γ-Thiapyrones by Diels-Alder/Retro-Diels-Alder Reaction of α-Pyrones with 5-H-1,2,3-Thiadiazoles

The efficient synthesis of γ-thiapyrones by a base-mediated Diels-Alder/retro-Diels-Alder reaction of α-pyrones with 5-H-1,2,3-thiadiazoles is reported herein. Thioketenes in situ generated from thiadiazoles as electron-poor dienophile and electron-rich 4-hydroxy-2-pyrones as dienes are conjunctively transformed into a series of γ-thiapyrones with broad functional group compatibility in good to excellent yields (35 examples, 67% average yield).

Enantioselective and collective total synthesis of pentacyclic 19-nor-clerodanes

We report herein the collective asymmetric total synthesis of seven pentacyclic 19-nor-clerodane diterpenoids, namely (+)-teucvin (+)-cracroson A, (+)-cracroson E, (+)-montanin A, (+)-teucvisin C, (+)-teucrin A, and (+)-2-hydroxyteuscorolide. An ytterbium-catalyzed asymmetric inverse-electron-demand Diels-Alder reaction of 4-methyl-2-pyrone with a chiral C5-substituted cyclohexa-1,3-dienol silyl ether is the key feature of the synthesis, which provides the common cis-decalin intermediate with five continuous stereocenters in excellent yield and stereoselectivity. From this diversifiable intermediate, the total synthesis of (+)-teucvin and (+)-2-hydroxyteuscorolide was realized in thirteen and eighteen steps, respectively. From (+)-teucvin, five other pentacyclic 19-nor-clerodanes were divergently and concisely generated through late-stage oxidation state adjustments.

Gram-Scale Enantioselective Synthesis of (+)-Lucidumone

The first enantioselective total synthesis of (+)-lucidumone is described through a 13-step synthetic pathway (longest linear sequence). The key steps involve the formation of a bridged bicyclic lactone by an enantioselective inverse-electron-demand Diels-Alder cycloaddition, C-O bond formation to assemble two fragments, and a one-pot retro-[4 + 2]/[4 + 2] cycloaddition cascade. The synthesis is scalable, and more than one gram of natural product was synthesized in one batch.