Asymmetric synthesis of cis-7-methoxycalamenene via the intramolecular Buchner reaction of an α-diazoketone.

The asymmetric synthesis of cis-7-methoxycalamenene 1 has been accomplished using the intramolecular Buchner reaction of α-diazoketone 7 as the key step in the synthetic route. Upon reduction of the equilibrating azulenone structure 8, the resulting azulenol 9 rearranges to dihydronaphthalene 10 containing the 6,6-membered bicyclic ring system characteristic of 1, by means of an acid-catalyzed aromatization process. Transformation of 10 to 1 is accomplished through a three-step reaction sequence.