Total syntheses of strained polycyclic terpenes

Diastereoselective Ring Expansion of Cyclic Ketones Enabled by HAT-Initiated Radical Cascade

Herein we disclose an iron-catalyzed method for stereoselective synthesis of multisubstituted cyclic ketones containing a synthetically challenging quaternary carbon from readily accessible β-vinyl keto esters in good yields. This cascade reaction is initiated by a hydrogen atom transfer (HAT) process, after which a Dowd-Beckwith-type ring-expansion reaction occurs. This strategic transformation offers access to synthetically valuable cyclic ketones bearing two contiguous stereocenters, including quaternary stereocenters, which hold paramount significance within the realm of synthetic chemistry.

The Awakening of a Sleeping Beauty: The ortho Photocycloaddition in the Total Synthesis of Protoilludane- and Prezizaene-Type ­Sesquiterpenes

Photochemical cascade (domino) reactions provide a unique opportunity for the construction of complex molecular architectures. Specifically, an intramolecular ortho photocycloaddition of 7-(alkenyloxy)-indanones triggers a sequence of consecutive reactions that can lead in a single operation to the complete skeleton of two important classes of sesquiterpenes: protoilludanes and prezizaenes. In the former case, two transformations follow the initial photocycloaddition, while in the latter case, there are three consecutive transformations, two of which are initiated by a photon. Remarkably, the reaction cascades proceed with exquisite diastereoselectivity, generating three (protoilludane) or five (prezizaene) stereogenic centers with defined relative configurations.

1 Introduction

2 First Encounter and Initial Studies

3 Protoilludane-Type Sesquiterpenes

4 Prezizaene-Type Sesquiterpenes

5 Enantioselectivity

6 Perspective and Summary