Synthesis of 9-Substituted-1,8-Dioxooctahydroxanthenes by an Efficient Iodine-Catalyzed Cyclization

Tandem Reactions for the Synthesis of High-Density Polycyclic Biofuels with a Double/Triple Hexane Ring

Synthesizing high-density fuels from non-food biomass is of great interest in the field of biomass conversion because they can increase the loading capability and travel distance of vehicles and aircraft as compared to conventional low-density biofuels (<0.78 g/cm³). In this work, we reported a new and facile strategy for the synthesis of high-density biofuels with polycyclic structures from lignocellulose-derived 5,5-dimethyl-1,3-cyclohexanedione and different aldehyde derivatives in two steps under mild reaction conditions, including a developed tandem reaction and a hydrodeoxygenation reaction. Theoretical approaches were used to estimate the fuel properties, which indicate that the obtained biofuels have a high density of 0.78-0.88 g/cm³ and high net heat of combustion (NHOC) values of 44.0-46.0 MJ/kg. A representative biofuel 3c was measured to have a high NHOC of 43.4 MJ/kg, which matched well with the calculated NHOC value of 44.4 MJ/kg, indicating the high accuracy of the theoretical approaches. This work is expected to provide a green strategy for the synthesis of polycyclic high-density biofuels with platform chemicals.

4a-Hydroxy-9-(4-hydroxyphenyl)-4,4a,5,6,9,9a-hexahydro-3H-xanthene-1,8(2H,7H)-dione

The title compound, C(19)H(20)O(5), was synthesized by the reaction of 1,3-cyclo-hexa-nedione and 4-hy-droxy-benzaldehyde in the presence of PdCl(2) and thio-urea. The tetra-hydro-pyran ring and the six-membered cyclo-hexene ring adopt envelope conformations, and the six-membered cyclo-hexane ring is in a chair conformation. The crystal packing is stabilized by classical inter-molecular O-H⋯O hydrogen bonds and weak C-H⋯O inter-actions.

9-(4-Chloro-phen-yl)-4a-hy-droxy-4,4a,5,6,9,9a-hexa-hydro-3H-xanthene-1,8(2H,7H)-dione

In the title compound, C₁₉H₁₉ClO₄, the central fused ring and the attached cyclo­hexene ring adopt envelope conformations, while the cyclo­hexane ring adopts a chair conformation. The crystal packing is stabilized by O—H⋯O hydrogen bonds, which link the mol­ecules into a chain along the b axis. Weak C—H⋯O bonds also occur.

Synthesis of cinnamyl ethers from α-vinylbenzyl alcohol using iodine as catalyst

Reactions of α-vinylbenzyl alcohol with other alcohols using iodine as a catalyst were investigated. The corresponding cinnamyl ethers were obtained as products. This suggested that α-vinylbenzyl alcohol was converted to cinnamyl ethers via 1-phenylallyl cation. Cinnamyl ethyl ether was obtained in 75% yield by the reaction of α-vinylbenzyl alcohol and ethanol in acetonitrile with iodine under the following conditions: temperature = 50 °C, molar ratio of α-vinylbenzyl alcohol:ethanol:iodine = 1:3.0:0.2, and time period = 6 h. Generally, the yields of the reactions using primary alcohols were higher than those using secondary and tertiary alcohols. Ether interchange also occurred by the reaction of α-vinylbenzyl alcohol and iodine, but proceeded smoothly only when an allyl group was used as the other substituent of the starting ether.