Masazumi Nakagawa

'Acetylene-cumulene' dehydroannulenes

ABSTRACT The synthesis of tetrasubstituted tetradehydro[18]− and [22]annulenes containing a diacetylene and a hexapentaene unit has been accomplished by reductive dehydroxylation of corresponding 18-membered and 22-membered cyclic glycols. On the basis of these studies, a general method of preparation of tetrasubstituted didehydro[4n + 2]annulenes containing an acetylene and a butatriene unit has been developed. The didehydro[4n + 2]annulenes (n = 3 ~ 7) were found to be diatropic and to have high conformational stability. The n.m.r. spectral properties of the didehydroannulenes have been discussed. The synthesis of didehydro[14]annulenes annelated with naphthalene or benzene has been achieved, and the effect of annelation on π-electron delocalization of the annulene ring has been discussed.

A naphtho-tri-t-butyltrisdehydro[16]annulene and related compounds

Abstract Synthesis of naphtho-tri- t -butyltrisdehydro[16]annulene containing a hexapentaene and an acetylene units has been described. It was found that the [16]annulene is less stable and the paratropicity is much stronger as compared with previously reported isomeric naphtho[16]-annulene containing a diacetylene and a butatriene linkage.

Novel linear relation in the electronic spectra of α,ω-diarylpoly-ynes

Abstract Twelve series of diarylpoly-ynes [Ar(CC) n Ar, n = 1 ∼ 6] bearing various kinds of aromatic terminal groups have been synthesized. It was found that the shifts of the longest-wavelength absorption maxima (λ L with the increase in the number of triple bonds ( n ) can be excellently expressed by the linear relationship: λ L = A n x + B The value of x varies from 1 to 2 [1 ⩽ x ⩽ 2] depending on the nature of the terminal groups and on the position of linking of the poly-yne chain, being x = 1 in the case of diphenylpoly-yne and x = 2 for 1.1′- and 9.9′-dianthrylpoly-ynes. The linear relation could be explained satisfactorily on the basis of HMO calculation assuming that the resonance integrals associated with triple and single bonds of the polyacetylene system should alter with n and be expressed by β cc = [1 + 1/( n + 4)]β and β cc = [1 - 1/( n + 4)]β, respectively. It was also shown that the wavenumbers of the longest-wavelength absorption maxima are in good correlation with the reactivity indices of the terminal aromatic hydrocarbon (Z r ) proposed by Brown.

Ion-pairing and ring current effects

Abstract A homologous series of [4n+2] annulenes reduced with alkali metals yields paratropic (4n)π-dianions. 1H NMR chemical shifts are most significant for a description of the relevant π-electron structures. However, the shift data turn out to reflect sensitively the ion-pairing. Therefore, the experimental conditions (counterion, solvent, temperature, organic ion) have been varied systematically, and a consistent description of the existing contact-solvent-separated ion pair equilibria (e.g. as a function of ring size, π-charge distribution etc) has been obtained. The interdependence of ion-pairing and ring current effects is discussed.

4-(t-butylthio)-3-buten-2-one. Synthon for α,β- and α,β,γ,δ-unsaturated aldehyde synthesis

Abstract A convenient synthesis of α,β- and α,β,γ,δ-unsaturated aldehydes using readily accessible 4-( t -butylthio)-3-buten-2-one as synthon was described.

Carotenoid synthesis with 4-(t-butylthio)-3-buten-2-one. A new synthesis of isorenieratene

Abstract Isorenieratene has been efficiently synthesized using 4-( t -butylthio)-3-buten-2-one as chain lengthening agent.

Annulenediones having quinonoid properties

Abstract Chemical and Electrochemical reductions of bisdehydro[14]- and [18]annu1ened1ones clearly revealed their quinonoid nature.

Fluorescence spectra characteristics of α,ω-Di-1- and 9-anthrylpoly-ynes

Abstract It has been found that the longest-wavelength of the absorption maxima (λ L ) in the electronic spectra of both the α,ω-diarylpoly-yne and polyene series varies linearly with the x th power of the number (n) of multiple bonds [λ L ∝ n x , the value of x changes with both the structure of the terminal groups and the position of substitution of the unsaturated chain, e.g. x = 2 for α,ω-Di-1-and 9-anthrylpoly-ynes( 1 n ,and 2 m n = 1–6)]. The results are different from the formerly accepted regularity (λ L 2 ∝ n ). The paper describes the fluorescence spectra characteristics of a series of 1 n and 2 n . The results of this investigation shows that, as in the case of the absorption spectra, both the excitation maxima ( λ ex ) and the emission maxima (λ em )in the fluorescence spectra of 1 n and 2 n have a linear relationship with n 2 (λ ex ∝ n 2 and λ em ∝ n 2 , respectively).

A novel acid-catalyzed transformation of octadienynedial derivatives to cyclopenta[b]-thiapyrans and cyclopenta[b]pyran.

Abstract Substituted 2,6-octadien-4-ynedial derivatives were synthesized, which give cyclopenta[b]thiapyran or cyclopenta[b]pyran derivatives by intramolecular cyclization.

Syntheses of an isoannelated annulene, a bisdehydro[14]annuleno[c]furan and bisdehydro[14]annulene derivatives

Abstract A bisdehydro[14]annuleno[c]furan, an isoannelated diatropic annulene, has been synthesized. Cyclic glycol, a precursor of the annuleno[c]furan, could be converted into bisdehydro[14]annulene derivatives under mild acidic conditions.