# Transformation of the cyclohexane ring to the cyclopentane fragment of biologically active compounds

## TL;DR

This review discusses methods to convert six-membered rings into five-membered cyclopentane structures, which are important in biologically active compounds.

## Contribution

The paper provides a comprehensive overview of recent strategies for ring contraction to synthesize functionalized cyclopentane/enones.

## Key findings

- Several synthetic methods and rearrangements for ring contraction are summarized.
- The review covers literature from the past 12 years, highlighting key developments in the field.
- Important exceptions from earlier works are included when relevant.

## Abstract

The review is devoted to strategies for contraction of six-membered cycles in the synthesis of functionalized cyclopentane/enones, which are biologically active compounds. The main synthetic methods of ring contraction (ozonolysis–aldol condensation, ozonolysis–Dieckmann reaction, Baeyer–Villiger cleavage–Dieckmann reaction) and rearrangements (benzil, semipinacol, with the participation of thallium- and iodine-based oxidants, photochemical, Wolff, Meinwald, Wagner–Meerwein and Favorskii) are presented. The review summarizes literature data covering the last 12 years, with some exceptions of earlier works due to the importance of the published information.