A Novel Approach to Synthesis of Tricyclic Diterpenoid

A novel approach has been found and the first total synthesis of (±)-Salvirecognine was accomplished by using it. In which intramolecular cyclization and Friedel-Crafts alkylation took place simultaneously to afford key intermediates for synthesis of aromatic tricyclic diterpenoids OMe PPA O O O OMe 1 2 Scheme 1 As shown in Scheme 1 intramolecular cyclization and Friedel-Crafts alkylation took place simultaneously when compound 1 was treated by PPA at 125 ℃. In which the i-pr…

A Novel Approach to Synthesis of Tricyclic Diterpenoid

A novel approach has been found and the first total synthesis of (±)-Salvirecognine was accomplished by using it. In which intramolecular cyclization and Friedel-Crafts alkylation took place simultaneously to afford key intermediates for synthesis of aromatic tricyclic diterpenoids Scheme 1As shown in Scheme 1 intramolecular cyclization and Friedel-Crafts alkylation took place simultaneously when compound 1 was treated by PPA at 125 ℃. In which the i-propyl group was introduced to the benzene ring directly and 2 was obtained in high yield. The structure of 2 was confirmed by X-ray crystallographic analysis.Scheme 2The mechanism of this novel approach might be as shown in Scheme 2. It's may be involved two times Friedel-Crafts alkylation and once fragmentation. We tried several different substrates and the new method was not only applicable in the conventional [6.6.6] tricyclic compounds but also suitable in [6.5.6] tricyclic compounds.By using the new approach as shown in Scheme 3 the first total synthesis of Salvirecognine 4,isolated from salvia recognit was achieved.Reagents and conditions: i) PPA, 125℃, 90%; ii) BBr3, CH2Cl2, 85%; iii) AlCl2H, 95%;Scheme 3