title: Differentiating mechanistic possibilities for the thermal, intramolecular [2 + 2] cycloaddition of allene-ynes.
abstract: Intramolecular [2 + 2] cycloaddition reactions of allene-ynes offer a quick and efficient route to fused bicyclic ring structures. Insights into the mechanism and regiochemical preferences of this reaction are provided herein on the basis of the results of quantum chemical calculations (B3LYP/6-31+G(d,p)) and select experiments; both indicate that the reaction likely proceeds through a stepwise diradical pathway where one radical center is stabilized through allylic delocalization. The influences of the length of the tether connecting the alkyne and allene and substituent effects are also discussed.
authors.affiliation: Department of Chemistry, University of California-Davis, One Shields Avenue, Davis, California 95616, USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Siebert
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Osbourn
authors.forename: Kay M
authors.initials: KM
authors.lastname: Brummond
authors.forename: Dean J
authors.initials: DJ
authors.lastname: Tantillo
mesh_terms: D000466:Alkadienes / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000138:chemical synthesis* / Q000737:chemistry; D003198:Computer Simulation; D003500:Cyclization; D015394:Molecular Structure; D011789:Quantum Theory; D013237:Stereoisomerism; D013696:Temperature
chemical_list: D000466:Alkadienes; D000480:Alkynes; D019086:Bridged Bicyclo Compounds, Heterocyclic