25394-27-8Relevant articles and documents
The charge delocalised beta,beta-carotene dication--preparation, structure elucidation by NMR and reactions with nucleophiles.
Lutnaes, Bjart Frode,Bruas, Liv,Kildahl-Andersen, Geir,Krane, Jostein,Liaaen-Jensen, Synnove
, p. 4064 - 4072 (2003)
The reaction between beta,beta-carotene and BF3-etherates has been investigated, leading to structural elucidation of the blue product, formed in appropriate organic solvents, as a symmetrical charge delocalised dication (lambda(max) 985 nm at room temperature in CHCl3) with considerable stability. The reaction, monitored by EPR studies at -25 degrees C, occurred via free radical intermediates. A C40H56BF3 intermediate was captured by EIMS. The detailed structure of the dication was established by COSY, HSQC, HMBC and 1D and 2D ROESY NMR techniques (600 MHz, CDCl3, -20 degrees C) leading to complete assignments of 1H and 13C chemical shifts and 3J(H,H) coupling constants. The effects of the two delocalised charges on chemical shift (charge distribution) and bond distance (3J(H,H)) were considered. The results are consistent with charge delocalisation mainly in the C-5-C-9 and C-5'-C-9' regions and with bond inversion to retro shifted double bonds in the central C-13-C-13' region. A convention for denoting the charge delocalisation and bond types is presented. The experimental results are discussed relative to previous theoretical calculations of the beta,beta-carotene dication structure. (All-E) and (15-Z)-beta,beta-carotene provided the same dication. The NIR spectra and stability of dications prepared in the same manner from the related carotenes 20,20'-dinor-beta,beta-carotene, heptapreno-beta,beta-carotene and nonapreno-beta,beta-carotene were examined for comparison. Reactions of the beta,beta-carotene dication with selected nucleophiles provided products including isocryptoxanthin, isocarotene and mutatochrome with H2O as nucleophile, and isocryptoxanthin methyl ether, 8-methoxy-7,8-dihydro-beta,beta-carotene and isocarotene with CH3ONa as nucleophile. The formation of these products is rationalised from the structure assigned to the dication.
Nucleophilic reactions of charge delocalised carotenoid mono- and dications
Kildahl-Andersen, Geir,Bruas, Liv,Lutnaes, Bjart Frode,Liaaen-Jensen, Synnove
, p. 2496 - 2506 (2007/10/03)
In the present study insight was gained on the larger complexity of cationic mixtures of diaryl (φ,φcarotene, isorenieratene) and aliphatic (Φ,Φ-carotene, lycopene) carotenes, prepared by reaction with BF 3-etherate, compared with β,β-carotene. Chemical reactions of the mono- and dications prepared in situ from the allylic carotenols β,β-caroten-4-ol (isocryptoxanthin) and β,β-carotene-4,4'- diol (isozeaxanthin), and from isorenieratene and lycopene were investigated using selected O, N and S nucleophiles; water, methanol, azide and thioacetate. In total 22, including 18 new, neutral carotenoid products were isolated and identified by VIS, MS and NMR (in part) spectroscopy. Their structures were compatible with the structures of the cationic intermediates. The formal addition of hydride to the various dications, required to rationalise minor reaction products, is discussed in terms of more likely hydrogen radical or proton transfer in cationic reactions. Extensive E/Z isomerisation was observed for all quenching products. The potential use of carotenoid cations for the synthesis of 4,(4')-substituted β,β-carotenes and 7-oxabicycloheptane derivatives is discussed.
Preparation and structure elucidation by NMR of the charge delocalised β,β-carotene dication
Lutnaes, Bjart Frode,Bru?s, Liv,Krane, Jostein,Liaaen-Jensen, Synn?ve
, p. 5149 - 5152 (2007/10/03)
The β,β-carotene dication (λmax 985 nm at room temperature) prepared by treatment of β,β-carotene with BF3-etherate had considerable stability. The reaction, monitored by EPR studies at -25°C, occurred by free radical intermediates. EIMS further revealed a C40H56BF3 intermediate. The detailed structure of the charge delocalised β,β-carotene dication was established by COSY, HSQC, HMBC and 1D and 2D ROESY NMR techniques (600 MHz, CDCl3, -25°C) leading to complete assignments of 1H and 13C chemical shifts and 3JH,H coupling constants. Considerable downfield shifts were observed relative to β,β-carotene. The results are consistent with charge delocalisation mainly in the C-5-C-9 and C-5′-C-9′ regions and with retro shifted double bonds in the central C-13-C-13′ region. The effect of the two delocalised charges on chemical shift (charge distribution) and bond distance (3JH,H) is discussed.
