A concise and efficient approach for the diastereoselective total synthesis of salvileucalin C, as well as their biosynthetically related diterpenoids salvileucalin D, salvipuberulin, isosalvipuberulin, and dugesin B, has been reported for the first time. The key features of the strategy are based on a Beckwith-Dowd ring expansion, a tandem diastereoselective Stille coupling/debromination/desilylation/lactonization reaction, and a photoinduced electrocyclic ring contraction.

Two new guaianolides, namely, 3beta,8alpha-dihydroxy-13-methoxyl-4(14),10(15)-dien-(1alphaH,5alphaH,6beta H,11betaH)-12,6-olide (1) and 3beta,8alpha-dihydroxy-13-methoxyl-4(14),10(15)-dien-(1alphaH,5alphaH,6beta H,11alphaH)-12,6-olide (2), together with six known guaianolides, 8-hydroxyzaluzanin C, austricin, chlorojanerin, cynaropicrin, chlorohyssopifolin E and chlorohyssopifolin A were isolated from the aerial parts of Saussurea alata. The structures were established mainly based on spectral analysis, especially 2D NMR techniques.

Diastereoselective Total Synthesis of Salvileucalin C. -The preparation of salvileucalin C (I) and its biosynthetically related diterpenoids salvileucalin D (II), salvipuberulin (III), isosalvipuberulin (IV) and dugesin B (V) is achieved. Asymmetric syntheses are in progress. -(FU, C.; ZHANG, Y.; XUAN, J.; ZHU, C.; WANG, B.; DING*, H.; Org. Lett. 16 (2014) 12, 3376-3379, http://dx.