Palladium-catalyzed allylic alkylation of allyl dienol carbonates: Reactivity, regioselectivity, enantioselectivity, and synthetic applications

For the past several years, the group has focused on the development of useful synthetic tools and on executing creative and efficient routes to biologically active natural products. In this context, we recently applied the palladium-catalyzed decarboxylative allylic alkylation reaction to a new class of substrates, namely allyl dienol carbonates. This method allowed a particularly straightforward access to a wide variety of heterocycles, including 2,4-disubstituted-, 2,3,4- and 2,3,5-trisubstituted-, and 2,3,4,5- tetrasubstituted furans and pyrroles, starting from simple and readily available substrates. An asymmetric version of this method was also developed and applied to the synthesis of enantiomerically enriched butenolides and butyrolactones bearing all-carbon α- and β-quaternary stereogenic centers, respectively. This asymmetric transformation was eventually used as a key step in the total synthesis of two natural products: (-)-nephrosteranic acid and (-)-roccellaric acid. This account summarizes the results of our endeavors. 1 Introduction 2 Palladium-Catalyzed Decarboxylative Allylic Alkylation of Allyl Dienol Carbonates 2.1 Synthesis of Polysubstituted Furans 2.2 Synthesis of Polysubstituted Pyrroles 3 Asymmetric Palladium-Catalyzed Decarboxylative Allylic Alkylation of Allyl Dienol Carbonates 3.1 Synthesis of Enantiomerically Enriched Butenolides 3.2 Synthesis of Enantiomerically Enriched Furanones 3.3 Synthesis of Enantiomerically Enriched Butyrolactones 3.4 Total Syntheses of (-)-Nephrosteranic Acid and (-)-Roccellaric Acid 4 Conclusion