A new synthesis of 12-O-methyl royleanone

Towards aflatoxins: a formal synthesis of aflatoxin B2

“…Gratifyingly the key reaction in our approach to 1, the benzannulation reaction between the Fischer carbene complex 2 and the disubstituted alkyne 3, proceeded without incident and afforded, after mild oxidative work-up, the target 1 in good overall yield, Scheme 2. 6 Crucially the regiochemical outcome of this reaction appeared to be in accord with the paradigm enunciated by Dötz 7 and Wulff. 8 Previously these groups had clearly shown that the differing steric bulk of the substituents on the alkyne had a controlling effect on the regiochemistry of its incorporation into the benzannulated product (i.e., i-Pr [R L ]>OMe [R S ]), Scheme 1.…”

“…In keeping with our earlier work on royleanone 6 we presumed that the methoxy substituent of 6 would act as the 'small' group and be incorporated proximal to the alkoxy group of the carbene complex 5 during the pivotal benzannulation step. That said we were also confident 10,11 that ester 7, the initial product of the benzannulation sequence, would cyclize to the lactone 8, thereby providing a route to the desired target 4, Scheme 4.…”

Enantioselective Synthesis of (+)-Royleanone from Sulfinyl Quinones

“…The main strategies used for the construction of the tricyclic framework are based on Robinson annulation, [7] and Friedel ± Crafts intramolecular acylation. [5c, 8] The Dötz reaction of a vinyl chromium carbene complex [9] has also been successfully used for this goal. More recently, a photochemical aromatic annulation has been applied to the synthesis of several diterpenoid quinones.…”

Cycloaddition and Electrocyclic Reactions of Vinylketenes, Allenylketenes, and Alkynylketenes

“…One example of the applications of this method is the synthesis of O-methyl royleanone (Scheme 178). 198 This process is judged to be somewhat shorter and higher-yielding than the vinylketene route shown in Scheme 174. 194 The Fischer carbene method does however lack the flexibility of routes utilizing free vinylketenes, which may be derived from diverse precursors and offer a wider variety of reaction pathways.…”