Dioxane, selective irradiation

Figure 9. Selective irradiation of dioxane. Homonuclear irradiation of a homogeneously broadened resonance at 67.9 MHz. Spectral details PW = 40 ysec (90° C), D2 = 10 sec, 4 scans accumulated, quadrature detection 15% acetone-dc,...

A direct solution to the problem of enantioselective furan-carbonyl photoproduct synthesis would require a photoaddition that proceeded with enantiofacial selectivity in the aldehyde or furan component and maintained the relative face selectivity that is intrinsic to the reaction. Preliminary work used host-guest chemistry to achieve this objective.In aqueous dioxane, a 1 1 1 inclusion complex of unmodified 3-cyclodextrin, furan and benzaldehyde is formed. Upon irradiation (Hanovia 450 W lamp, Vycor filter), a rapid photoaddition occurs to afford a photoproduct of 10-20% ee. 

Preliminary runs with solvents such as dioxane and THF proved to be far less effective than a mixture of 3 1 acetic acid (AcOH) and ethanol (EtOH). Both AcOH and EtOH effectively couple with microwave irradiation and had the advantage that the starting materials were soluble under the reaction conditions at elevated temperatures, while the DHPM products 35 were comparatively insoluble at room temperature facilitating product isolation. Having selected the solvent, the next... 

Several X-ray fluorescence speclromelric delerminations of lechnelium were reported. Hie lines X.,2=0.67927 A, X,i=0.67493 A, X, i=0.6()141 A, and X,(2= 0.59018 A can be used for detection and determination of the element 30,31]. From neutron irradiated molybdenum milligram quantities of Tc could be isolated and detected by the Ka and Kjn lines [46]. Because of its simplicity and selectivity, an X-ray fluorescence method was developed for the determination of technetium in solution. At concentrations of less than 1.0 mg Tc per ml no interelcment effects were observed. Therefore, it is possible to ascertain technetium in its compounds without their prior decomposition, provided the compounds are soluble in water or dioxane. The detection limit is about 4- lO g Tc [47. For the determination of Tc in nuclear fuel processing wastes by X-ray fluorescence, a rapid, simple, and accurate method was reported [48]. 

Excitation of the ketone (226) brings about a 1,7-hydrogen transfer to afford the biradical intermediate (e.g., 227). Cyclization within this species yields the alkenyl-tetrahydrofurans (228) and (229) in the yields and ratios shown. The cyclization process is reasonably selective in that the geometry of the double bond is retained in the cyclized product. This was demonstrated for the enone (230) (a cis trans mixture of ratio 1 3), which gave the cyclized products (231—234) (Scheme 16). Two principal products (235, 15%) and (236, 60%) are obtained from irradiation of the ketone (237) in dioxan solution. " Two minor products (238)... 

Figure 5. Plot of peak frequencies in the 1H off-resonance selectively decoupled 13C spectra of NAD+ as a function of position of irradiation in the 1H spectrum, expressed in ppm from internal dioxan. The positions of the peaks in the 1H noise decoupled 13C spectrum are shown by lines on the ordinate and the position of the proton peaks by lines on the abscissa. The arrows t indicate the point of collapse of the 1 3C doublet and the connection between a given 1 3C peak and proton peak. The errors in the position of measurements are indicated by the size of the points except near the cross-over positions where the errors are larger ( 0-15 ppm). (Taken from Birdsall et al., 1972a.)...

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