Synthesis of the Alleged Natural Monoterpenoid α-Santolinenone

Article abstract of DOI:10.1002/hlca.19840670511

Authentic α-santolinenone ( = (+)-(4R)-1(7)-p-menthen-2-one; (+)-1) is made available for the first time in 30 percent overall yield from (+)-(4R)-p-menthene ((+)-2) via the diastereomeric allylic alcohols (+)-4a/(+)-4b, which are oxidized to (+)-1 with Ag2CO3/Celite.Yields are good, except for the last stage; indeed, only alcohol (+)-4a, with equatorial OH-group, undergoes oxidation, and (+)-1 is partly substracted via a hetero Diels-Alder dimerization giving a mixture of the diastereomeric dihydropyrans (+)-5a/(+)-5b.When Cr(VI) reagents are used, (+)-4a/(+)-4b mainly give phelandral (6) and carvotanacetone (7).MnO2 reacts too sluggishly with (+)-4a/(+)-4b.A camphor pyrolyzate, previously thought to be 1 must be a different compound, probably 7.