CYCLIC PHENYLBORONATES OF ECDYSTEROIDS AS PRODUCTS OF REGIOSPECIFIC REACTION WITH PHENYLBORONIC ACID

The diol system in the side-chain of ecdysteroids reacts with phenylboronic acid under formation of cyclic esters. Phenylboronates of ecdysteroids I - V were prepared. The regiospecific reaction course was confirmed by H-1 NMR spectra of the products. The reaction conditions were studied for 20-hydroxyecdysone (1). The phenylboronate can be prepared in high yields even in aqueous solutions. The liberation of the ecdysteroid I from the corresponding phenylboronate VI was performed using various reagents - diols or carboxylic acids.