# MontmorilloniteEco-friendly and Effective Catalyst in the Synthesis of Biologically Active Compounds with Bicyclo[3.3.1] Moiety

## TL;DR

This paper explores using montmorillonite clay as an eco-friendly catalyst to efficiently produce bioactive bicyclic compounds with potential fragrance and estrogen-like properties.

## Contribution

The study introduces acid-treated montmorillonite as a cost-effective and green alternative for synthesizing bicyclo[3.3.1] compounds.

## Key findings

- Acid-treated montmorillonite achieved >85% limonene conversion and >70% selectivity in 24 hours.
- Higher temperatures improved conversion but reduced selectivity for the target compound.
- Montmorillonite outperformed heteropoly acid-modified catalysts in cost-effectiveness and selectivity.

## Abstract

Prins cyclization is a key method for synthesizing oxygen-containing
heterocycles with biological activity involving the reaction of alkenes
and aldehydes under mild acidic conditions. This process is valuable
for producing compounds such as 2,2,6-trimethyl-4-(1-propenyl)-3-oxabicyclo[3.3.1]­non-6-ene,
a bioactive bicyclic ether synthesized from limonene and crotonaldehyde.
Compounds with bicyclo[3.3.1]­nonene structures are interesting due
to their fragrance properties and potential estrogen receptor activity.
This study evaluates montmorillonite (MMT), a low-cost, environmentally
friendly clay, as a heterogeneous acid catalyst for this reaction.
Acid treatment of MMT (treated with HNO3, HCl, H2SO4, and H3PO4) had a positive influence
on limonene conversion compared with nonmodified MMT, and limonene
conversions >85% and selectivity >70% were obtained (24 h).
Reaction
parameters such as temperature, solvent, catalyst amount, and limonene-to-crotonaldehyde
ratio significantly influenced conversion and selectivity. Higher
temperatures and lower crotonaldehyde ratios improved the achieved
limonene conversion, though selectivity decreased with temperature.
Montmorillonite-supported heteropoly acids (HPW and HPMo) increased
conversion but reduced selectivity and showed inefficient catalyst
utilization at higher loadings. The initial reaction rate increased
and selectivity decreased with catalyst acidity. Overall, acid-treated
MMTs are more effective and economical than heteropoly acid-modified
variants, offering a viable path for synthesizing bicyclic ethers
via green chemistry.