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.
Some bicyclic gem-dichlorocyclopropanes (Ia through Id) and gem-chlorofluorocyclopropanes (IIa through IId) were prepared by the addition of dichloro- and chlorofluorocarbene, respectively, to the appropriate cyclic olefins. The reduction of these dihalocyclopropanes with tri-n-butyltin hydride gave the corresponding monochloro- (IIIa through IIId) or monofluorocyclopropanes (IVa through IVd) in fairly good yields. When treated with an excess of hot quinoline, the endo-chloro isomers of IIa, IIb, IId, IIIa, IIIb, and IIId were converted to their ring expansion products, whereas their exo-chloro isomers were recovered unchanged. In contrast, the exo-chloro isomers of IIe and IIIc decomposed more readily than their endo-chloro isomers under similar conditions. These results were discussed on the concept of a concerted disrotatory process.
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