Keiji Shingu

Sensitivity of circular dichroism of β-diketones to minute changes in the orientation of chromophores

Abstract Three optically active diastereomers of 3,8-di- t -butylspiro[4.4]nonane-1,6-dione have been prepared. Their c.d. spectra showed very different features to each other in spite of the same configuration at their spiro centers, showing the sensitivity of c.d. to minute changes in the orientation of chromophores.

Optically active spiro[4.4]nonane derivatives: syntheses and circular dichroism of bis-αβ-unsaturated ketones

(5S)-Spiro[4.4]nona-3,8-diene-2,7-dione (1) and (5S)-spiro[4.4]nona-2,7-diene-1,6-dione (2) have been prepared; the c.d. of (1) in the longest wavelength π→π* region shows the opposite sign to that predicted by exciton theory as in the case of spiro[4.4]nona-1,6-diene (3).

Stereospecific, photochemical rearrangement of 1,1′-spirobiindene and 1,1′-spirobi[benzindene]S

The photochemical rearrangement, of optically active 3,3′-di-t-butyl-1,1−spirobiindene and −1,1′-spirobi[benzindene]s afforded, respectively, 5,7-di-t-butylbenzo[c]fluorene and its dibenzo derivatives with high stereospecificity.

Proposal of a symmetry rule for β,γ-unsaturated ketones

A symmetry rule for the sign of Cotton effect of β,γ-unsaturated ketnoes in n → π* region has been proposed and this rule can correctly predict the sign of c.d. even for the ketones to which the generalized octant rule could not be applied.

Effect of spiroconjugation on the UV and CD spectra of 1,1′-spirobiindene

Abstract U.v. and c.d. spectra of 1,1′-spirobiindene were theoretically explained based on the composite molecule method. The effect of spiroconjugation was shown to appear markedly in the 1 L a region of indene, making a large splitting of this band, as was expected from PE spectra.

Molecular structures of three diastereoisomers of 3,3′-di-t-butyl-1,1′-spirobi-indan

Crystal structures of the three diastereoisomers (+)-(1R,3S,3′S)-(I), (±)-rel-(1R,3R,3′R)-(II), and (±)-rel-(1R,3R,3′S)–(III) of the title compound, C25H32, have been determined by X-ray analysis. Crystals of (I) are orthorhombic, space group P212121, a= 12.412(1), b= 14.842(1), c= 11.287(1)A, Z= 4. Crystals of (II) are monoclinic, space group P21/c, a= 16.230(1), b= 11.719(1), c= 11.400(1)A, β= 110.23(1)°, Z= 4. Crystals of (III) are monoclinic, space group P21/c, a= 13.220(1), b= 13.877(1), c= 11.897(1)A, β= 109.81(1)°, Z= 4. The structures were solved by the direct method and refined by a block-diagonal least-squares technique to R= 0.032 for (I)(1 455 reflections), 0.034 for (II)(2 146), and 0.044 for (III)(2 437). The relative configuration between the chiral centres in each isomer was as expected from 1H n.m.r. data. The cyclopentene rings are all in envelope conformations, and the tertiary butyl groups adopt quasi-equatorial orientations in agreement with 1H n.m.r. data except the one in (II), which takes a quasi-axial orientation. The dihedral angles between the two benzene ring planes are 69.5(1), 91.4(1), and 94.9(1)° for (I)–(III), respectively. Calculation for the optimal structure using the MM2 program showed that the discrepancy in the form of (II) can be ascribed to a crystal packing effect.

Absolute configuration and conformation of 1,1′-spirob[benz[g]indan]

Three diastereomers of (1S) 3-3′-di-t-butyl-1,1′-spirobi [benz[f] indan] have been prepared. In the 1Bb region all the isomers showed typical c.d. couplets of negative sign, reflecting the identity of configuration at the spiro center irrespective of their different conformations.

Bicyclo[3.3.0]octenol as an effective tool for the determination of absolute configuration of chiral acids. The absolute configuration of aryl-t-butylacetic acid

Abstract (+)- endo - cis -Bicyclo[3.3.0]oct-7-en-2-ol gave good optical yields in the kinetic resolution of aryl- t -butylacetic anhydrice, establishing the absolute configuration of t -butyl-α-naphthylacetic acid as ( S ) - (+).

Conformational dependence of circular dichroism of 1,1′-spirobi[benz[e]indan]

Three diastereomers of 3,3′-di-t-butyl-1,1′-spirobi[benz[e]indan], (lS,3R,3′R)-(1a), (1S,3S,3′S)-(1b), and (1S,3R,3′S)-(1c), have been prepared; c.d. spectral evidence is presented for their different conformations.

Optically active spiro[4.4]nonane derivatives: syntheses and circular dichroism of homoconjugated dienes and diketimine derivatives

(+)-(5S)-Spiro[4.4]nona-1,6-diene (1), (+)-(5S)-6-methylenespiro[4.4]non-1-ene (2), (+)-(5R)-1,6-dimethylenespiro[4.4]nonane (4), and four diketimine derivatives from (-)-(5S)-spiro[4.4]nonane-1,6-dione (5) were prepared; their chiroptical behaviour in the π→π* region was consistent with expectations based on the exciton model, except for (1).