# Synthesis of an A/B-cis-Fused Cyclopenta[b]fluorene (6/5/6/5) Ring System for Embellicine A via the Eight-Membered Silylene-Tethered IMDA Reaction

## TL;DR

Scientists developed a new method to synthesize a complex ring structure found in embellicine A using a silylene-tethered Diels–Alder reaction.

## Contribution

A novel eight-membered silylene-tethered IMDA approach for constructing a cis-fused cyclopenta[b]fluorene ring system.

## Key findings

- The A/B-cis-fused tetracyclic compound was obtained with complete stereoselectivity.
- Functional group manipulations led to the synthesis of a fully elaborate embellicine tetracyclic fragment.

## Abstract

The first synthesis of an A/B-cis-fused
cyclopenta­[b]­fluorene (6/5/6/5) ring system was successfully
achieved
via an intramolecular Diels–Alder (IMDA) reaction of an eight-membered
silylene-tethered precursor. In this key step, a significant conformational
change in the diene moiety was achieved by introducing an eight-membered
silylene tether, and the desired A/B-cis-fused tetracyclic
compound was obtained with complete stereoselectivity. After several
functional group manipulations on the D-ring, a fully elaborate tetracyclic
fragment of embellicines was successfully synthesized.