Recent Progress in Accessing Multi-functionalized Caged Hydrocarbons: En Route to Highly Functionalized Saturated (Bio)isosteres of Benzene Rings

Abstract Recently, many saturated bioisosteres of the benzene ring have been developed, and their applications in drug development have been evaluated. Most of these bioisosteres are caged hydrocarbons, which have rigid skeletons and three-dimensional spaces. Recent efforts to synthesize these caged hydrocarbons have enabled access to multi-functionalized congeners that are expected to be (bio)isosteres of multi-functionalized benzenes. This short review summarizes recently reported methods for obtaining multi-functionalized (typically more than disubstituted) caged hydrocarbons. 1 Introduction 2 Proposed Structures of Caged Hydrocarbons as Saturated (Bio)isosteres of the Benzene Ring: A Brief Summary 3 Access to Multi-functionalized Caged Hydrocarbons: De Novo Synthetic Approaches 3.1 Bicyclo[1.1.1]pentanes (BCPs) 3.2 Bicyclo[2.1.1]hexanes (BCHs) 3.3 Bicyclo[3.1.1]heptanes (BCHeps) 3.4 Others 4 Access to Multi-functionalized Caged Hydrocarbons: C–H Functionalization 5 Conclusion