Synthesis of Bio-Based Methylcyclopentadiene from 2,5-Hexanedione: A Sustainable Route to High Energy Density Jet Fuels.

The sustainable, bio-based, platform chemical, 2,5-hexanedione [HD ( 1 )], was efficiently converted to methylcyclopentadiene [MCPD ( 4 )] through a three-step process consisting of intramolecular aldol condensation, catalytic chemoselective hydrogenation, and dehydration. Base-catalyzed aldol condensation of 1 resulted in the formation of 3-methyl-2-cyclopenten-1-one [MCO ( 2 )], which was then converted to 3-methyl-2-cyclopenten-1-ol [MCP ( 3 )] by chemoselective reduction with a ternary Ru catalyst system [RuCl 2 (PPh 3 ) 3 /NH 2 (CH 2 ) 2 NH 2 /KOH]. The hydrogenation proceeded with 96% chemoselectivity. 3 was then dehydrated over AlPO 4 /MgSO 4 at 70 °C under reduced pressure to yield 4 , which can undergo an ambient temperature [4+2]-Diels-Alder cyclization to generate dimethyldicyclopentadiene (DMDCPD), a commodity chemical useful for the preparation of high-performance fuels and polymers. Through this approach, advanced jet fuels and materials can be conveniently produced from sustainable cellulosic feedstocks.