Synthetic Studies Of Rubrolone Aglycon

Rubrolone, a red alkaloid isolated from Streptomyces echinoruber in 1978, is non-toxic for use as food colors. It consists of sugar and aglycon which contains 7/5/6 tricycle system with a cycloheptatrienone ring. This unique structure brings a challenge for us.In the first part, our previous study endeavored toward synthesis of Rubrolone aglycon with the key 7/5/6 tricycle skelecton by using Suzuki coupling reaction, diazo transfer reaction and Buchner expansion reaction. Fortunately, we confirmed that the structure of Buchner reation product is 6/6/6 tricycle by X- ray diffraction.In the second part, we adjusted the synthetic strategy via replacing substituents to reduce the electron density, synthetize double activated diazo and Bamford-Stevens cyclopropanation cascade reaction to attempt to expansion reaction respectively, but it didn’t work. Finally, we prepared the α-bromodiazo substrate to conduct Buchner expansion reaction in the presence of Rh2(mandelate)4, the product with 7/5/6 tricycle framework was achieved through preliminary identification, this will be helpful for our subsequent work.