Regiospecific photoisomerization of fluorinated (E,E)-1,4-diphenyl-1,3-butadienes

Photoisomerization of five fluorinated E,E-1-(R-phenyl)-4-phenyl-1,3-butadienes in solution (R = 1: p-monofluoro, 2: m,m′-difluoro, 3: m,m′,p-trifluoro, 4: o,o′,m,m′-tetrafluoro, 5: o,o′,m,m′,p-pentafluoro) was investigated via direct irradiation. Our results indicated that cis-trans photoisomerization of the fluorinated 1,4-diphenyl-1,3-butadienes in the excited singlet state took place exclusively at the CC bonds closer to the fluorine substituents.     

Liquid chromatographic determination of sotalol in plasma and urine employing solid-phase extraction and fluorescence detection

A liquid chromatographic method using a solid-phase extraction procedure for the quantification of sotalol in plasma and urine is described. Sotalol is eluted from an extraction column with ethyl acetate-acetonitrile (1:2) and, after separation by reversed-phase high-performance liquid chromatography on a mu Bondapak C18 column, is quantified by fluorescence detection at excitation and emission wavelengths of 240 and 310 nm, respectively. The method has been demonstrated to be linear over the concentration ranges 10-6000 ng/ml in plasma and 0.5-100 micrograms/ml in urine. Mean inter-assay accuracy of the method for plasma ranged from 93 to 100% and for urine from 102 to 114%; precision ranged from 0.5 to 1.6% for plasma over a concentration range of 200-4000 ng/ml and for urine from 0.7 to 2.0% at concentrations of 2-50 micrograms/ml. Mass spectrometry confirmed the presence of sotalol in isolated chromatographic fractions of plasma and urine extracts from subjects given sotalol orally.     

Regiospecific topochemical reactions controlled by trifluoromethyl directing groups

A parallel, offset-stacked orientation was found in the crystal packing of E,E-1,4-di(o-trifluoromethyl)phenyl-1,3-butadiene. UV-irradiation of the powered crystalline sample resulted in a quantitative conversion to a single [2 + 2] cycloaddition product.     

Regioselectivity of E/Z photoisomerization of fluorinated cisoid (1E,3E)-1,4-diphenylbutadienes via direct irradiation

Direct irradiation of the 1E,3E isomers of six cisoid fluorinated butadienes in an organic solvent at room temperature showed a predominant formation of the 1Z,3E isomers.     

New aspects of diphenylbutadiene photochemistry. Regiospecific hula-twist photoisomerization

In EPA glass at liquid nitrogen temperature, the E,E isomer of diphenylbutadiene (DPB) was photostable, while both the Z,E and Z,Z isomers underwent selective HT isomerization at center 1 giving the stable conformer of the double-bond isomerized trans product. That HT-1 was involved rather than the OBF process was shown by results of o,o'-dimethyl-DPB. Formation of unstable trans product corresponded to simultaneous configurational and conformational isomerization. The regioselectivity was found not sensitive to a substituent effect, as shown by the similar reactivity in p,p'- or o,o'-bistrifluoromethyl-DPB.     

Trifluoromethyl groups in crystal design of 1,4-diphenyl-1,3-butadienes for topochemical [2 + 2] photodimerization

[structure: see text] UV irradiation of the powdered crystalline sample of each of three (E,E)-1,4-di(trifluoromethyl-substituted)phenyl-1,3-butadienes (1-3) was found to yield a single [2 + 2] cycloaddition product in the solid state. Moreover, upon irradiation, the crystalline samples of two (E,E)-1,4-di(trifluoromethyl- and fluorine-substituted)phenyl-1,3-butadienes (4, 5) undergo a similar conversion to afford a [2 + 2] cycloaddition product, respectively. Our observations suggest that trifluoromethyl groups can be used to direct 1,4-diphenyl-1,3-butadiene molecules to form a parallel, offset-stacked orientation suitable for topochemical [2 + 2] cycloaddition.