Jūro Ojima

Stereodynamics of N,N-dialkyl-9-triptycylamines

Abstract Stereodynamics of a series of N , N -dialkyl-9-triptycylamines is studied by 1 H and 13 C dynamic NMR spectroscopy. The energy barriers to the observed internal motions are governed by the eclipsing interaction between an N -alkyl group and a benzene ring of the triptycene moiety together with the intrinsic barrier to nitrogen inversion.

A synthesis of a doubly-bridged [24] annulene

Abstract Reductive coupling of 1, 6-bis(2-formylvinyl)cyclohepta-1, 3, 5-triene with a low-valent titanium reagent afforded a paratropic bismethano [24] annulene.

The synthesis of diphenyltrideca-, -pentadeca-, -heptadeca-, and -nonadecafulvene derivatives

Abstract Title fulvenes were synthesized through the reaction of the large-membered annulenones with diphenylketene, and examination of 1H-NMR spectra suggests that the fulvenes are atropic.

Configurational and conformational isomerization of 9,14-dimethyl-10, 12-bisdehydro[19]annulenone in neutral and acidic solutions

Dissolution of the title compound (1) in CF3CO2D-CD2Cl2 formed a cationic species which showed extensive isomerization. 1 recovered by neutralization existed as a mixture of isomers different from the initial one indicating that the latter formed under kinetic control.

The synthesis of 2-ethoxy-6,11-dimethyl-7,9-bisdehydroaza[14]annulene and its benzannelated derivatives

Title azaannulenes were synthesized starting from annulenones, and the 1H-NMR spectra are discussed in connection with tropicity of these annulenes.

Synhtesis of 2-ethoxy-6,11-dimethyl-7,9-bisdehydroaza[16]annulene and 2-ethoxy-8,13-dimethyl-9,11-bisdehydroaza[18]annulene

Abstract Title azaannulenes, the paratropic and diatropic vinylogues of pyridine, were synthesized starting from the annulenones.

Annelated dehydroannulenes fused with azulene ring. The synthesis of bisdehydro[14]- and -[16]annuleno[a]azulene

Abstract 10,12-Bisdehydro-3-isopropyl-9,14-dimethyl[14]- and -11,16-dimethyl[16]annuleno[a]azulene in which the conjugated 14- and 16-membered rings are fused to azulene ring, have been synthesized. It was found that the fusion of azulene ring suppresses the diatropicity of [4n+2], 14π-electron system to a smaller extent than benzene ring.

Unusual formation of a methano-bridged didehydro[20]annulenedione. A highly diatropic, dicationic 18π-electron species in D2SO4

An intramolecular coupling of 1,6-bis(5-oxohepta-1,3-dien-6-ynyl)cyclohepta-1,3,5-triene under Glaser conditions affords 12,15-dichloro-13,14-didehydro-1,6-methano[20]annulene-11,16-dione, which exhibits strong diatropicity in D2SO4, suggesting the formation of the highly delocalized dicationic species.

Synthesis and properties of methano-[12]-, -[18]-, -[20]-, -[22]-, -[24]-annulene and dimethano-[20]- and -[24]-annulene

Reductive couplings of the vinylogues of cyclohepta-1,3,5-triene-1,6-dicarbaldehyde with a low-valent titanium reagent afforded the corresponding monomeric or dimeric products, i.e. singly bridged or doubly bridged annulenes in most cases. These annulenes showed diatropicity or paratropicity, depending on the number of peripheral conjugated π-electrons. The 1H n.m.r. spectra of the methanoannulenes showed a larger temperature-dependency than those of the closely related tetradehydromethanoannulenes, reflecting the lower planarity and the larger conformational mobility of the molecular skeleton in the former compounds.

5,10-Dimethyl[13]annulenone: The first monocyclic annulenone larger than tropone

5,10-Dimethyl[13]annulenone, the first monocyclic annulenone larger than tropone, was synthesized by catalytic partial hydrogenation of 5,10-dimethylbisdehydro[13]annulenone. The 1H NMR data indicate that the compound is completely atropic. Molecular mechanics studies suggest the nonplanarity of the ring and thus the lack of peripheral conjugation.