Synthetic approaches to phomactins: Novel oxidation of homoallylic alcohols using tetra- n -propylammonium perruthenate

Previous studies of a synthesis of phomactin A had resulted in the synthesis of a 15-methylenebicyclo[9.3.1]pentadecadiene. The next step in the synthesis was to be the epoxidation of this methylenecyclohexane that was hoped would lead to a 1-(hydroxymethyl)cyclohexene by rearrangement of the exocyclic epoxide, but the epoxidation was difficult to carry out regioselectively on advanced intermediates. However, oxidation of a 15-methylenebicyclo[9.3.1]pentadeca-3,7-dien-14-ol using tetra-n-propylammonium perruthenate and N-methylmorpholine-N-oxide led to conversion of this homoallylic alcohol into the corresponding 14-oxobicyclo[9.3.1]pentadeca-1(15),3,7-triene-15-carboxaldehyde in one step. Reduction of this using DIBAL-H gave a promising intermediate for a synthesis of a phomactin. The scope of this oxidation of homoallylic alcohols was briefly investigated.