A Novel Approach to Combretastatins: From trans-Epoxide to CA-4 and Its Dioxolane Derivative

Total syntheses of borolithochromes H1, H2, I1, and I2

Total syntheses of borolithochromes H1, H2, I1, and I2, the red pigments isolated from fossils of Jurassic putative red alga Solenopora jurassica, have been achieved. The naphthoquinone possessing a chiral sec-butyl side chain has been synthesized from (S)-2-methylbutanol. The Diels-Alder reaction of the chiral naphthoquinone and the previously reported diene was followed by one pot S-methylation/intramolecular Corey-Chaykovsky reaction/epoxide rearrangement to provide the benzo[gh]tetraphene skeleton. Complexation of the resulting ligand with trimethyl borate and the following O-demethylation furnished a 1:1 mixture of borolithochromes I1 and I2, which were separated by HPLC using CHIRALPAK IC® to afford optically pure borolithochromes I1 (6) and I2 (7). On the other hand, borolithochromes H1 and H2 were not separated by HPLC in our laboratory. Fortunately, the mixture of the methyl ethers of borolithochromes H1 and H2 were separated and O-demethylation with magnesium iodide furnished optically pure borolithochromes H1 (4) and H2 (5).

Total Syntheses of Borolithochromes A, D and G

Total syntheses of borolithochromes A, D and G, red pigments isolated from fossils of Jurassic putative red alga Solenopora jurassica, have been achieved. The benzo[gh]tetraphene skeletons of the borate ligands in these substances were constructed using Diels-Alder reactions of aryl dienes with naphthoquinone, followed by intramolecular Corey-Chaykovsky reactions. Complexation of these ligands with trimethyl borate generated homocomplexes, which upon sequential O-demethylation produced borolithochromes A and G. In the route to borolithochrome D, a heterocomplex was prepared by stepwise complexation of the ligands with 2-(dimethylamino)ethyl dimethyl borate. The strategy devised to accomplish the first total synthesis of borolithochromes A, D and G should be applicable to the preparation of other borolithochromes as well as spiroborates possessing two fused polycyclic aromatic ligands.

One-pot synthesis of epoxides from benzyl alcohols and aldehydes

A one-pot synthesis of epoxides from commercially available benzyl alcohols and aldehydes is described. The reaction proceeds through in situ generation of sulfonium salts from benzyl alcohols and their subsequent deprotonation for use in Corey–Chaykovsky epoxidation of aldehydes. The generality of the method is exemplified by the synthesis of 34 epoxides that were made from an array of electronically and sterically varied alcohols and aldehydes.