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.

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.

Synthesis of Karrikinolide Using the Aldol-Type Acetal Addition Reaction.

A short step total synthesis of karrikinolide has been achieved. Both α and α' positions of -acylated acetol were alkylated by the boron-mediated aldol-type acetal addition reaction. The one-pot sequence including the Arbuzov reaction, intramolecular Horner-Wadsworth-Emmons reaction, acidic hydrolysis of acetals, and pyran formation provided karrikinolide.