hexane, and 7-bromo-7-fluoro-2-oxanorcarane, were reduced with tri-n-butyltin hydride a t 20-175' to yield the corresponding monofluorocyclopropanes. It has been found, by isolating the geometrical isomers of each substrate and reducing them separately, that in most cases the configuration of the starting material is retained during the reduction, but the stereospecificity tends to be decreased by the increase of the reaction temperature, the decrease of the hydride concentration, and the presence of ring oxygen in bicyclic structure. These results are reasonably explained by postulating a pyramidal structure for the cyclopropyl radical. (7) (a) J. D. Graham and H. T. Rogers, ibid., 84, 2249 (1962); (b) W. G. (8) K.The nmr spectra of the cyclobutane protons of the head-to-head syn dimer of coumarin and the head-to-head anti dimer of N-methylcarbostyril have been analyzed. The analysis has demonstrated that it is possible to correlate the structure and stereochemistry of these photodimers with the coupling constants. A similar analysis of the photodimers of 6-chloro-and 6-methylcarbostyril has been performed and their structure and stereochemistry have been assigned.
Aus den stereoisomeren Formen von 1‐Chlor‐1‐fluor‐cyclopropanen(Ia)‐(Ic) bzw. (IIb)‐(IIe) mit bekannter Zusammensetzung der Isomerengemische sowie der Tetramethylverbindung (Ia) = (IIa) werden mitTributylzinnhydrid (III) die entsprechenden Fluorcyclopropane (IVa) =(Va) bzw. (IVb)‐(IVe) bzw. (Vb)‐(Ve) erhalten.
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