Degradations and Rearrangement Reactions
2.7
409
⊡ Scheme 57
ized in polar nitromethane containing BF 3 ·OEt 2 , the bromide 272 is practically inert [217]
( > Scheme 57).
The silylated ketose 274 slowly anomerizes in the presence of TASF by way of the keto-form
[218]. The thioglycoside 276 anomerizes in the presence of a catalytic amount of IDCP [219].
Under PTC conditions, the β-chloride 278 also anomerizes [220]. Anomerization of 280
to the α-form 281 via an open-chain zwitterionic intermediate has been suggested [221]
( > Scheme 58).
An investigation of the time course of the anomerization of β-iodide 282 has been carried
out using 1 H-NMR spectroscopy [222]. The NMR titration method to measure the shift of
2.7
409
⊡ Scheme 57
ized in polar nitromethane containing BF 3 ·OEt 2 , the bromide 272 is practically inert [217]
( > Scheme 57).
The silylated ketose 274 slowly anomerizes in the presence of TASF by way of the keto-form
[218]. The thioglycoside 276 anomerizes in the presence of a catalytic amount of IDCP [219].
Under PTC conditions, the β-chloride 278 also anomerizes [220]. Anomerization of 280
to the α-form 281 via an open-chain zwitterionic intermediate has been suggested [221]
( > Scheme 58).
An investigation of the time course of the anomerization of β-iodide 282 has been carried
out using 1 H-NMR spectroscopy [222]. The NMR titration method to measure the shift of