Haru Ogawa

Novel rearrangement of twisted 2,4-di-alkyl 2-trans-4-trans pentadienals: An approach to cyclopentenones based on molecular mechanical consideration

Rearrangement of 2,4-di-trans-pentadienals IVa-d was described as a consequence of the successive alkyl substitutions on the C-2 and C-4 positions. 1H-FT nmr spectroscopy suggested that the reaction involves ketene VIII as an intermediate.

The synthesis of 6,7-benzo-4,9-oxido[11]annulenone and aromatic 6,7-benzo-4,9-oxido[11]annulenyl cations☆

Abstract The titled annulenone 6 , the first benz-annelated 11-membered fully conjugated ketone, has been prepared by the aldol type condensation of 3-benzoxepin-2,4-dialdehyde 3 and dimethyl acetone-dicarboxylate. Some evidence for the nonaromatic character of 6 could be obtained from the NMR and IR spectra as well as protonation behaviour of 6 . The NMR spectrum of 6 in conc H 2 SO 4 confirmed the presence of an aromatic 1-hydroxy-6,7-benzo-4,9-oxido[11]annulenyl cation 7 . 6,7-Benzo-4,9-oxido-1-hydroxy-1-homo[10]annulene 11 was prepared by the NaBH 4 reduction of 6 . The treatment of 11 with CF 3 COOH regenerated another completely delocalized [11]annulenyl cation 12 . The pk R + of 12 was obtained as −4·1, spectrophotometrically. The electronic spectra of these novel cations ( 7 and 12 ) were found to be similar to those of 4,5-(2′,3′-naphtho)tropylium cations ( 13a and 13b ), respectively.

Bridging effects of furan ring incorporated in the perimeters of a bisdehydro[16]annulene and a bisdehydro[18]annulene: syntheses of 1:14-epoxy-6,8-bisdehydro[16]annulene and 1:16,10:13-diepoxy-4,6-bisdehydro[18]annulene

Aus Furan-2,5- dialdehyd (I) erhalt man mit dem Phosphoniumsalz (II) den homologen Dialdehyd (III), der mit weiterem Phosphoniumsalz (IV) zum Di-acetylen (V) fuhrt.

Preparation of oxygen-bridged aza[15]- and aza[17]annulene dicarboxylates by intramolecular azide cyclization

Abstract Aza[15]annulene dicarboxylate ( 12 ), aza[15]annulenone dicarboxylate ( 13 ) and aza[17]annulene dicarboxylate ( 19 ) were prepared. Compound ( 12 ) proved to be paratropic, and ( 19 ) proved to be diatropic.

Chemical transformations of 4:7,10:13-diepoxy[15]annulenone by carbonyl transposition reactions

Abstract The titled annulenone 1 could be converted into new annulenones 3 and 8 by carbonyl transposition reactions. Compound 8 can be regarded as the first 14π hydroxy-enone as a higher homolog of tropolone (6π) and hydroxy[11]annulenones (10π), and was proved to be aromatic.

A simple methodology for aza-annulene synthesis: preparation and propreties of 2,15-diethoxycarbonyl-4,7:10,13-diepoxy-2-cis,8-cis, 14-cis-aza[15]annulene

The synthesis and properties of the titled compound (9) are described; (9) was prepared by the thermolysis of the vinyl azide (5) in 70% yield, and no furopyrrole derivatives were formed.

Synthesis of a bridged homo[15]annulenium ion

Aus dem Annulenon (I) erhalt man mit Dimethylsulfoniummethylid das Homoannulenon (II), das durch Decarboxylierung und Reduktion mit Boranat in das Diol (III) ubergefuhrt wird.

Diepoxy[15]annulenones undergo photochemical carbonyl-O/divinyl ether-O transportation rearrangements: mechanistic probing of the rearrangement sequences facilitated by 13C/17O NMR spectroscopy

On irradiation, diepoxy[15]annulenone 1 and monobromo-diepoxy[15]annulenone 2 undergo an intriguing rearrangement, whereby all of the ether and carbonyl oxygens of 1 and 2 can travel freely and change their positions in the rings to give 15 position isomers in all.

Photocyclic processes of an oxygen-bridged [15]annulenyl ion, whose state-to-state changes are very similar to those of bacteriorhodopsin

The photochemical behaviour of the hydroxy[15]annulenyl ion TH+ and ethoxy[15]annulenyl ions (TEt+) is described; TH+ participates in a bacteriorhodopsin-like photocyclic process, giving very similar state-to-state changes in the transitions it undergoes.

4 : 7,10 : 13-Diepoxy[15]annulenones exchange their oxygen bridges on irradiation: 17O NMR spectroscopic and chemical verification of the exchanges

A 17O NMR study shows that, on visible light irradiation, the unsubstituted 4 : 7,10 : 13-diepoxy[15]annulenone 1 undergoes a degenerate rearrangement, by which the carbonyl oxygen of 1a is interchangeable with the furan ring oxygens in 1b and in 1c; the 2,15-dimethyl analogue 2 undergoes similar oxygen-bridge exchange to give two positional isomers BC and DE in two different ways (i.e. via photo-irradiation and via a protonation–deprotonation sequence).