Ready access to alkylidenecyclopentenones by Nazarov cyclization/β- elimination of 2-hydroxyalkyl-1,4-dien-3-ones

Article abstract of DOI:10.1002/ejoc.201301537

Cross-conjugated dienones bearing α-hydroxyalkyl substituents readily undergo Nazarov cyclization followed by deprotonation of the resulting cyclopentenyl cation, and β-elimination of the exocyclic hydroxy group to form alkylidenecyclopentenones in moderate yield. The deprotonation step occurs with complete regioselectivity opposite to the hydroxyalkyl substituent, with preferential introduction of an endocyclic olefin. The transformation is tolerant of a variety of substituents and occurs under relatively mild conditions. Alkylidenecyclopentenones are readily accessed in moderate yields from α-hydroxy-substituted dienones by Nazarov cyclization followed by β-hydroxy elimination. The regioselectivity of the initial deprotonation of the Nazarov intermediate is remarkably high and leads to an endocyclic alkene opposite to the hydroxy subsitutent. Copyright