6.7- Dimethoxycoumarin

Farinotti, R., Siard, Ph., Bourson, J., Kirkiacharian, S., Valeur, B., and Mahuzier, G., 4-bromomethyl-6, 7-dimethoxycoumarin as a fluorescent label for carboxylic acids in chromatographic detection, /. Chromatogr., 269, 81, 1983. 

This method suffered from sensitivity problems initially as the bile-acid molecules lack a chromophore, but did offer the distinct advantage that conjugated bile acids could be determined without hydrolysis. The sensitivity issue was addressed by use of fluorescent derivatives such as dimethoxycoumarin esters with a C18 reverse phase column and were able to resolve endogenous mixtures of bile acids. The combination of hplc and mass-spectroscopy detection has further improved the sensitivity along with providing specific identification, important as the resolution of bile acids by hplc is not as good as capillary column glc. ... 

Transition from a chromenoid skeleton to a benzofuran has also been achieved by other means. We may mention the photooxidation of rotenone814 and the preparation of 5,6-dirnethoxybenzofuran by electronic impact on 6,7-dimethoxycoumarin.815 The Koelsch reaction is kindred it converts couinarine into 2,3-dihydrobenzofuran derivatives.816... 

Several approaches have been made to calculate 13C chemical shifts of coumarins by MO methods. Good correlations were found between the 13C chemical shift values of coumarin (also protonated) and the n charge densities calculated by the CNDO/2 method [962], and of coumarins with it charge densities calculated by the Hiickel MO method (which, however, fails for methoxylated coumarins) [965]. Chemical shifts of mono- and dimethoxycoumarins have been correlated with parameters determined by refined INDO MO calculations, in which n bond orders, atom-atom polarizabilities, excitation energies and electron-nucleus distances were taken into consideration [966], In 3-substituted 4-hydroxy and 4-hydroxy-7-methoxycoumarins chemical shifts were found to be related to Swain and Lupton s parameters iF and M [388], according to equation 5.4 (SE = Substitution Effect) ... 

A good correlation was found between the HMO atom-atom polarizabilities n j and substitution effects (SE) for mono- and dimethoxycoumarins [965] ... 

Cycloaddition is, in general, an effective way of generating cyclobutane rings. The lactone (304) is converted in this way on irradiation into both head-to-tail (305) and head-to-head (306) dimers.248 Direct irradiation of 5,7-dimethoxycoumarin in acetonitrile or benzene similarly affords the syn head-to-tail dimer via the singlet excited state, whereas... 

Addition to six-membered oxygen heterocycles is also common. The photocycloaddition of 5,7-dimethoxycoumarin to tetramethylethylene has been described,269 and 4-hydroxycoumarin (326) undergoes facile addition to cyclohexene on direct irradiation to give the cyclobutane (327)270 analogous additions to a variety of other alkenes have been reported, and the cycloaddition of 4-methoxycoumarin to 2-methylpropene has been employed in a synthesis of l,2-dihydrocyclobuta[c]coumarin.271 Photoaddition of the 1,2-bisenol lactone (328) to tran.s-stilbene yields propellane (329),272 and [ 2 + 2] cycloaddition is observed along with other competing photoreactions on irradiation of chromone in the presence of alkenes.273... 

A mixture of 6,7-dimethoxycoumarin (1 mmol) and Lawesson s reagent 1 (0.5 mmol, in the case of esters, 0.8 mmol), was taken in a glass tube and mixed thoroughly with a spatula. The glass tube was then placed in an alumina bath inside the microwave oven (900 W) and irradiated for 3 min. On completion of the reaction, followed by TLC examination, the colored material was dissolved in di-chlorometliane and adsorbed on silica gel and purified by silica gel column chro-... 

BMDMC 4-bromomethyl-6,7-dimethoxycoumarin MP Mechanical pulverization (e.g., ball mill)... 

SYNS AESCULETIN DIMETHYL ETHER 6,7-DLMETHOXYBENZOPYRAN-2-ONE 6,7-DIMETHOXYCOUMARIN ESCOPARONE ESCULETIN DIMETHYL ETHER SCOPARON SCOPARONE... 

Limettin (5,7-Dimethoxycoumarin) is obtained from West Indian lime oil and various citrus oils. 

Dimethoxycoumarin (149) resulted in syn head-to-tail photodimer products excited either by simultaneous TPA (650 nm excitation, pulse width 120 fs, repetition rate 1 kHz) or by common OP broadband UV excitation [487]. Syn head-to-head and syn head-to-tail photodimers (Fig. 3.61) were formed in 1 3 and 1 2.8 ratios under OP (broadband UV) and TP (650 nm, 120 fs) irradiation in anisole. Furthermore, a tenfold increase of the quantum yield was observed under TP excitation ( 10 2) compared to broadband UV irradiation ( 10-3). 

Dimethoxycoumarin undergoes a two-photon (2 + 2)-dimerization when irradiated at 650 nm using a pulsed laser source. Two-photon irradiation has been used to regenerate the coumarin from the (2 -l- 2)-dimers. Comins and his co-workers described an approach to the synthesis of the lupin alkaloid (22). This is approached using intramolecular (2 + 2)-cycloaddition using a suitably sub-... 

In a more rigorous way, Grigor and Webb (65) reproduced the l3C shieldings of coumarin and some mono- and dimethoxycoumarins by refined INDO MO calculations and found that, in addition to atom-atom polarizabilities (14) and ti bond orders (20), other factors such as excitation energies and electron-nucleus distances, (r 3)2P, play an important role in the determination of the 13C chemical shifts of these compounds. 

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