title: No acid required: 4π and 6π electrocyclization reactions of dienyl diketones for the synthesis of cyclopentenones and 2H-Pyrans.
abstract: The 1,6-conjugate addition of nucleophiles to dienyl diketones produces either cyclopentenone or 2H-pyran products with high selectivity through either Nazarov (4π) or 6π electrocyclization, respectively. The outcome of the reaction is dependent upon the nature of the nucleophile used. Nucleophiles that are anionic or easily deprotonated exclusively produce cyclopentenones via Nazarov cyclization, whereas the neutral nucleophile DABCO promotes 6π cyclization to afford 2H-pyrans. Experimental evidence is presented for both retro-4π and -6π electrocyclization in these systems, lending support to the bifurcated mechanistic hypothesis proposed for these cyclizations.
authors.affiliation: Department of Chemistry, University of Rochester , Rochester, New York 14627, United States.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Jacob
authors.forename: Joshua L
authors.initials: JL
authors.lastname: Brooks
authors.forename: Alison J
authors.initials: AJ
authors.lastname: Frontier
mesh_terms: D000143:Acids / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D003517:Cyclopentanes / Q000138:chemical synthesis* / Q000737:chemistry; D007659:Ketones / Q000737:chemistry*; D015394:Molecular Structure; D011714:Pyrans / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000143:Acids; D003517:Cyclopentanes; D007659:Ketones; D011714:Pyrans; C013905:cyclopentenone