Journal of the American Chemical Society, Vol.117, No.46, 11421-11425, 1995
Face Selection in Additions to the Trigonal C-2 Site in Quaternized 5-Azaadamantane Derivatives
The quaternary N-allyl bromide salt 5 of allyl alpha-[2-(5-azaadamantylidene)]benzyl ether upon warming gave the Claisen rearrangement products 6 is the ratio E/Z = 93:7. The epoxidation of the N-oxide 8 of 2-methylene-5-azaadamantane 7 with m-CPBA gives rise to the two diastereomeric epoxides 9 in the ratio E/Z = 19:81. Reaction of the methyl iodide salt of this olefin with bromine in water produces the E- and Z-dibromides 10 in the ratio 74:26 as well as the corresponding glycols 12 in the ratio 86:14. The same reaction in methanol gives the E- and Z-isomers of 10 alone, in the ratio of 35:65. The interpretation is that, in all of these reactions, the trigonal carbon preferably undergoes addition at that face which is antiperiplanar to the more electron-rich vicinal bonds, and does so by margins substantially in excess of those observed with the corresponding 5-fluoroadamantanes. This fact lends further strength to our previously drawn conclusion that hyperconjugative transition state stabilization is the principal factor in the electronic component of face selection.