246
2
General Synthetic Methods
⊡ Scheme 37
⊡ Scheme 38
⊡ Scheme 39
A gem-difluoride is formed when a ketone or aldehyde is treated with DAST, as outlined in
the reaction of 68 to 69 ( > Scheme 38) [60].
For the synthesis of 71 from 70, N,N-diethyl-α,α-difluoro-(m-methylbenzyl)amine (DFMBA)
is used to avoid the unexpected migration of the methoxy group from the 1- to 5-position when
DAST is used ( > Scheme 39) [63].
2.3 Ring-Opening Reactions
2.3.1 Opening of Epoxide Rings
As an alternative practical method, the opening of epoxides by halide ions has often been used
for introducing halogens, especially fluorine, into sugar molecules. Sodium iodide, magnesium
bromide, and hydrogen halides (HCl, HF) are frequently used as halogen sources [64,65].
2
General Synthetic Methods
⊡ Scheme 37
⊡ Scheme 38
⊡ Scheme 39
A gem-difluoride is formed when a ketone or aldehyde is treated with DAST, as outlined in
the reaction of 68 to 69 ( > Scheme 38) [60].
For the synthesis of 71 from 70, N,N-diethyl-α,α-difluoro-(m-methylbenzyl)amine (DFMBA)
is used to avoid the unexpected migration of the methoxy group from the 1- to 5-position when
DAST is used ( > Scheme 39) [63].
2.3 Ring-Opening Reactions
2.3.1 Opening of Epoxide Rings
As an alternative practical method, the opening of epoxides by halide ions has often been used
for introducing halogens, especially fluorine, into sugar molecules. Sodium iodide, magnesium
bromide, and hydrogen halides (HCl, HF) are frequently used as halogen sources [64,65].