Cyclopentanoids from phenol. Part 5. Terminally functionalised 2- and 3-alkyl-4-hydroxycyclopent-2-enones. A versatile approach to prostanoids

Abstract

Terminally functionalised 3-alkyl-4-hydroxycyclopent-2-enones are prepared by conjugate addition–elimination reactions of magnesiocuprate reagents with ethers of 3-chloro-4-hydroxycyclopent-2-enone. The side-chain functionality can be modified either selectively, or simultaneously with modification of the nucleus. Stereospecific transposition of the ring-oxygen functions converts these compounds into terminally functionalised 2-alkyl-4-hydroxycyclopent-2-enones which are important intermediates in prostanoid synthesis. Thus the 2-substituted cyclopentenone (2) is prepared in ca. 60% yield from the 3-chlorocyclopentenone (7), itself available in four steps from phenol.