The Stabilized 5-Hexenyl Radicals

At that time, products were identified by hydrolysis and comparison with authentic crystallized material, and hence it was possible that the corresponding Cy5H escaped detection. Nevertheless, two conclusions arose, the first one being that these reactions could be of synthetic value, and the second being that, in this case, the cyclized products were the Cy6 ones. Later, it was shown by chromatographic analysis that some (Cy5) products were also produced but it was confirmed that the very major products are indeed the (Cy6) type, in clear contradiction of the results obtained by Lamb and Walling described above (Section ii.l). 

Within a few years, a large number of papers devoted to intramolecular free radical addition reactions appeared, particular attention often being given to the matter of ring size. Before discussing these results we shall first endeavor to analyze and rationalize the behavior of 5-hexenyl radicals. 

In a short note dealing with the cyclization of 5-hexenyl radicals Julia reported that Cy 6 formation apparently was favored only when the initial 

Even if we accept the foregoing schemes it is still necessary to explain why the (CyS) compounds are the favored ones when the addition is an irreversible one. 

Three explanations have been advanced. These are based on steric, stereoelectronic, and entropic arguments but, as will be seen, they are probably not as mutually exclusive as might at First be thought. 

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