Titanocene(III) mediated radical cyclizations of epoxides for the synthesis of medium-sized cyclic ethers

Cp2TiCl-Promoted Endo-Trig Radical Cyclization to Six- and Seven-Membered Carbocycles: Synthesis of (±)-Isoclavukerin A

A systematic study is undertaken to investigate the less explored endo-trig radical cyclization in activated olefin-appended epoxides using Cp2TiCl. The radical generated by the Ti(III)-promoted reductive opening of the epoxy ring promptly underwent endo-trig cyclization, giving access to differently 1,3-disubstituted six- and seven-membered carbocycles in good yields and diastereoselectivity. This protocol was successfully employed in the construction of 5,7- and 6,7-fused bicyclic frameworks entailing a de novo synthesis of (±)-isoclavukerin A belonging to tri-nor-guaiane class of sesquiterpene natural products in eight simple steps from commercially available starting materials. Besides the Ti(III)-mediated reaction serving as a key step in the synthesis, a sequential [2,3]-sigmatropic rearrangement/syn-elimination of an allyl sulfenate intermediate successfully rendered the highly constrained diene moiety in the hydroazulene core of the target molecule.

DFT study on the [4+4] domino cycloaddition of ynones with benzylidenepyrazolones to access eight-membered cyclic ethers: effects of DBUvs.Et3N

The difference in the catalytic activity of bases is primarily attributed to their electron-donating ability (t-BuO⁻> DBU > Et₃N).

Unorthodox synthesis, biological activity and DFT studies of novel and multifunctionalized naphthoxocine derivatives

A new promising protocol has been developed for the synthesis of scarce oxocine derivatives 3a-e and 6 through addition of amine-based nucleophiles such as hydroxylamine hydrochloride, primary amine and hydrazide to chromonylidene benzothiazol-2-ylacetonitrile 2 in refluxing dioxane under metal free reaction conditions in moderate to good yields. Other nitrogen nucleophiles such as piperidine, hydrazine and thiosemicarbazide failed to afford the corresponding oxocinols, and instead pyridine derivatives 7, 8 and 10 were obtained exclusively. Predictive study for the biological activities using PASS (prediction of activity spectra for biologically active substances) online software showed optimistic activities for oxocinols 3a-e in the treatment of cancer, influenza A and microbial infections. Additionally, DFT studies of oxocine derivatives 3a-e and 6 indicated the presence of required thermodynamics parameters for the application in dye-sensitized solar cells (DSSCs).

A Concise and Efficient Total Synthesis of α-Mangostin and β-Mangostin from Garcinia Mangostana

The concise, efficient synthesis of α-mangostin is described in eight simple steps with 8.3% overall yield. Highlights include a practical approach to construct the isopentene groups and other diverse groups at C–2 and C–8 of the xanthene skeleton through Claisen rearrangement and Wittig reaction. Meanwhile the first total synthesis of β-mangostin is presented with a similar approach.