A Route to Carbasugar Analogues - Jonathan Clayden - The ...

Chapter 1: Introduction
conditions, although the data allow few direct comparisons to be made, and it is
unclear if the results presented have been optimised.
Miyano et al. propose a SET mechanism for this dearomatisation stating that
carbanions have an electron donating ability which follows Bn > allyl- >> t-Bu > i-Pr
> Bu >> Ph, and is consistent with their results. 19 They cite Bartoli as the source of
this data, who had used oxidation potentials of Grignard reagents to propose electron
donating ability i-Pr > Bn ≥ Et > Me >>Ph; 20 contradicting Miyano. Miyano also cites
Yamamoto, who used ionisation potentials of organostannanes to infer an electron
donating ability allyl >> n-Bu > vinyl. 21 Aside from the data appearing to disagree
with the conclusions of the authors, they also fail to note Yamamoto’s advice that
“there must be an argument against extending this substituent order of ionization
potential for organotins to that for organocoppers,” when applying these data.
Further evidence of an SET mechanism is evidenced in the especially high yield
resulting from addition trimethylsilyllithium (entry j), a species which has been used as
single electron reductant for the production of EPR spectra. However, many other
dearomatisations have occurred with silicon nucleophiles in good yield (vide infra)
without stimulating thoughts of an SET reaction.
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