Facile multistep synthesis of isotruxene and isotruxenone.

Three multistep approaches toward facile syntheses of isotruxene (1) and isotruxenone (3) are reported. The ortho-para conjugated backbone in the precursor 4 was constructed by either Co-catalyzed [2 + 2 + 2] cyclotrimerization or the [4 + 2] Diels-Alder reactions. The regioselectivity of the triple intramolecular Friedel-Crafts acylation of 4 plays the key role in determining the overall yield. Compared to the previous one-step method, the current approaches are more efficient in terms of product yield (27-36% vs 4-18%) and purification (i.e., free of column chromatography).