Graduate Thesis Or Dissertation
 

Substituent control in the oxy-Cope rearrangements of 1-vinyl-trans-cyclotridec-3-en-1-ol systems

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  • The thermal and anionic rearrangements of substituted 1-vinyltrans- cyclotridec-3-en-l-ol compounds have been studied to determine what effects substituents would have on the sigmatropic shift when placed on the two positions of the 1-vinyl group. For the thermal rearrangements, the a-substituted vinyl-trans-cyclotridecenols gave both the [3,3] and [1,3] shift products of rearrangement. On the other hand the β-methyl and trimethylsilyl groups gave a high periselective control favoring the [1,3] shift siloxy-Cope ring expansion relative to the [3,3] shift. A rather unusual result was obtained for the β-isopropyl case. The products obtained from its rearrangement were trienes resulting from loss of the trimethylsiloxy group. The effect of substituents on the control of periselectivity in the case of anionic rearrangements was much less than for the thermal ones. The α-substituted vinyl-trans-cyclotridecenols gave products of rearrangement comparable to that of the unsubstituted case, studied earlier. However the study of the anionic rearrangements of the β-substituted alcohols were found to be of interest, since their products of rearrangement would throw considerable light on the nature of the mechanism as to whether it is concerted or non-concerted. Thus treatment of cis and trans β-methyl vinyl-cyclotridecenols with KH in HMPA, gave along with the [1,3] shift product, both the [3,3] shift diastereomers. The formation of both diastereomers from the rearrangement of either the cis or trans alcohols indicates that for a concerted mechanism, both the chair and the boat transition states would be involved. On the other hand the possibility of the mechanism being non-concerted could not be ruled out, since substantial evidence pointing towards a nonconcerted ring fragmentation-recombination mechanism was obtained from the rearrangement of the 0-isopropyl substituted alcohol. Finally, the synthetic utility of the [1,3] shift ring expansion product, obtained from the thermal rearrangements of alcohols 2c and 2d was demonstrated by its conversion to a natural product, muscone.
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