When two become one

 

When two become one: An enantiospecific synthesis of hispidanin A, a dimeric diterpenoid from Isodon hispida, was achieved with a longest linear sequence of 12 steps and 6.5 % overall yield. Key component are the use of the diterpenoids (+)-sclareolide and (+)-sclareol as starting materials to prepare the key intermediates totarane (1) and labdadienolide (2), and intermolecular Diels–Alder reaction of 1 with 2 to give hispidanin A.

Please see  https://web.pkusz.edu.cn/yang/110/ for the detail.