Synthesis of Bridged Oxabicycles via Cascade Reactions involving O-Acyloxocarbenium Ion Intermediates

Discovery of a Formal Dyotropic Rearrangement during Acid-Mediated Dioxabicyclo[4.2.1]nonanone Formation

A new reaction mechanism for the construction of dioxabicyclo[4.2.1]nonanone skeletons via a cation cascade has been proposed and examined by DFT and ab initio computations. This mechanism features the following steps: (1) intramolecular Friedel-Crafts-type cyclization with a methyl oxocarbenium cation formed by carboxylate disconnection, (2) electron-rich aromatic ring assisted methoxide loss followed by lactone formation, and (3) stepwise dyotropic rearrangement resulting in skeletal isomerization from a dioxabicyclo[3.2.2]nonanone to the dioxabicyclo[4.2.1]nonanone product observed experimentally. The high regioselectivity and driving force for the overall rearrangement were rationalized, and Lewis and Brønsted acid mediated reactivities were compared.

Recent asymmetric synthesis of natural products bearing an α-tertiary amine moiety via temporary chirality induction strategies

Covering: 2013 to 2023The α-tertiary amine moiety is a common structural motif in natural alkaloids and is frequently associated with intriguing biological activities and inherent synthetic challenges. A major hurdle in the total synthesis of these alkaloids is the asymmetric construction of the α-tertiary amine moiety. Temporary chirality inductions have been effective strategies employed to address this issue, particularly in natural product synthesis. The temporary chirality induction strategies in α-tertiary amine synthesis can be broadly classified into three categories based on the types of temporary chirality involved: Seebach's self-regeneration of stereocenters (SRS), C-to-N-to-C chirality transfer, and memory of chirality (MOC). This review highlights the recent advancements in temporary chirality induction strategies for the total synthesis of α-tertiary amine-containing natural products between 2013 and 2023.