Total synthesis of (±)-tanshinol B, tanshinone I, and (±)-tanshindiol B and C.

A concise and efficient approach was established for the divergent total synthesis of (±)-tanshindiol B and C and tanshinone I from a ubiquitous ene intermediate in 1-2 steps. This critical intermediate was derived from (±)-tanshinol B, which was synthesized in 50% overall yield over 3 steps using an ultrasound-promoted cycloaddition as a key step. Compared to a previously reported strategy, our approach is more step-economic, thus greatly improving the synthetic efficiency. The bioactivity evaluation indicates that the diol stereochemistry of the tanshidiols has an impact on the EZH2 inhibitory activity.