Pmfm. Bastiaansen et al., CHEMICAL CONSEQUENCES OF LONG-RANGE ORBITAL INTERACTIONS IN CHOLESTANE-3,7-DIOL MONOSULFONATE ESTERS - A 7-CENTER FRAGMENTATION, Journal of organic chemistry, 61(3), 1996, pp. 859-867
The manifestation of through-five-bond interactions in the reactions o
f the rigid 1,5-diol monosulfonate esters (1-3), having an ideal all-t
rans geometry of the sigma-relay, with sodium tert-amylate is investig
ated. It has been shown that the deprotonation of the alcohol group in
2 and 3, which results in an increased electrofugal ability of this g
roup, finds expression in a seven-center fragmentation. This fragmenta
tion also illustrates that effective through-five-bond interactions ex
ist between the alcoholate group and the carbocationic center which is
generated during the heterolysis. The reaction outcome of mesylate 1
does not indicate effective through-bond interactions, and only elimin
ation is observed. This difference can be attributed to the alkyl subs
tituents on the gamma- and alpha-positions to the mesylate group in 2
and 3, respectively, which stimulate the seven-center fragmentation. T
hough a reasonable amount of fragmentation product is obtained from 3,
the through-five-bond interaction is not strong enough to dominate th
e reaction course completely and typical El-like processes, i.e., elim
ination and rearrangement, are competitive. As expected, only a 1,2 Me
-shift is observed in the reaction of the axial mesylate 4 where a gau
che interaction is present in the geometry of the sigma-relay. The pre
sence of through-bond interactions in the reactions of 3 and 4 becomes
apparent by comparison of the reactivity of 3 and 4 with their O-sily
lated analogs 5 and 6.