title: Ring size and substituent effects in oxyanion-promoted cyclizations of enyne-allenes: observation of a Myers-Saito cycloaromatization at cryogenic temperature.
abstract: A series of acetoxy-substituted enyne-allenes, fused to cyclopentene and cyclohexene ring systems, were synthesized and treated with methyllithium to generate the corresponding enolates. It was found that whereas the cyclohexannulated examples underwent either C2-C7 (Myers-Saito) cycloaromatization or C2-C6 (Schmittel) cyclization depending on their terminal subsituents, the cyclopentannulated examples either failed to cyclize altogether or underwent C2-C7 cyclization. Both of these results lie in contrast to the behavior of their benzannulated analogues, which underwent exclusive C2-C6 cyclization independent of substituents. These findings are rationalized on the basis of both ring strain effects and the steric encumbrance of the terminal alkynyl and allenyl subsituents.
authors.affiliation: Department of Chemistry and Cancer Center, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, USA.
authors.forename: Michelle K
authors.initials: MK
authors.lastname: Waddell
authors.forename: Tefsit
authors.initials: T
authors.lastname: Bekele
authors.forename: Mark A
authors.initials: MA
authors.lastname: Lipton
mesh_terms: D000466:Alkadienes / Q000737:chemistry*; D000475:Alkenes / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry*; D000838:Anions; D003080:Cold Temperature; D003500:Cyclization; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry; D013696:Temperature
chemical_list: D000466:Alkadienes; D000475:Alkenes; D000480:Alkynes; D000838:Anions; D009942:Organometallic Compounds; C520093:methyllithium