title: Ene-diamine versus imine-amine isomeric preferences.
abstract: Cyanide-catalyzed aldimine coupling was employed to synthesize compounds with 1,2-ene-diamine and alpha-imine-amine structural motifs: 1,2,N,N'-tetraphenyletheylene-1,2-diamine (13) and (+/-)-2,3-di-(2-hydroxyphenyl)-1,2-dihydroquinoxaline (17), respectively. Single-crystal X-ray diffraction provided solid-state structures and density functional theory calculations were used to probe isomeric preferences within this and the related hydroxy-ketone/ene-diol system. The ene-diamine and imine-amine core structures were calculated (B3LYP/6-311++G(d,p)) to be essentially identical in energy (DeltaG = 0.2 kcal/mol in favor of the imine-amine, within the error of the calculation). However, additional effects-such as pi conjugation-in 13 render an ene-diamine structure that is slightly more stable than the imine-amine tautomer (14) (DeltaG = 0.2-0.7 kcal/mol, within the error of the calculation). In contrast, the intramolecular hydrogen bonding present in 17 significantly favors the imine-amine isomer over the ene-diamine tautomer (18) (DeltaG = 7.2-8.9 kcal/mol). For both 13 and 17, the optimized calculated structures (B3LYP/6-31+G(d')) are identical to those observed by single-crystal X-ray diffraction.
authors.affiliation: Texas A&M University, College Station, Texas 77843-3255, USA.
authors.forename: B Jesse E
authors.initials: BJ
authors.lastname: Reich
authors.forename: Erin E
authors.initials: EE
authors.lastname: Greenwald
authors.forename: Aaron K
authors.initials: AK
authors.lastname: Justice
authors.forename: Brittany T
authors.initials: BT
authors.lastname: Beckstead
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Reibenspies
authors.forename: Simon W
authors.initials: SW
authors.lastname: North
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Miller