Heterogeneous catalysis for transformation of biomass derived compounds beyond fuels: Synthesis of monoterpenoid dioxinols with analgesic activity

• Addition reaction of cis-verbenol oxide to benzaldehyde is catalyzed by solid acids.
• The target product is a dioxinol compound with analgesic activity.
• Highest yield with Fe-modified beta zeolite with a large benzaldehyde excess.

Catalytic synthesis of a dioxinol compound, (2S,4aR,8R,8aR)-4,4,7-trimethyl-2-phenyl-4a,5,8,8a-tetrahydro-4H-benzo[d][1,3]dioxin-8-ol, exhibiting analgesic activity was demonstrated over Fe-modified beta zeolite. During interactions between cis-verbenol oxide and benzaldehyde, two main reactions occurred. In the first reaction, namely isomerization of verbenol oxide both cyclopentenic hydroxyketone, oxetane as well as a cyclohexyl compound, (1R,2R,6S)-3-methyl-6-(prop-1-en-2-yl)cyclohex-3-ene-1,2-diol were formed. In the second parallel reaction the target compound was generated. The highest yield of the target compound was achieved in the reaction between verbenol oxide and benzaldehyde at their molar ratio of 1:133 with the bifunctional iron modified Fe-H-Beta-150 catalyst at 70 °C giving a much higher yield than reported earlier in the literature, being 46 mol-% at complete conversion of verbenol oxide.

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