396
2
General Synthetic Methods
⊡ Scheme 31
⊡ Scheme 32
been found in the fluorination reaction of the thiosugar furanose 138 [119]. It is known that
the sulfur(IV) fluoride/hydrogen fluoride system also promotes such ring-contraction reactions [120]. On Friedel–Craft reaction of the thiopentosyl bromide 140, a ring-contraction
process occurs [121]. The per-O-alkylated glycoside 142 is converted into the δ-lactone 143
with concomitant ring-contraction to furnish product 144 [122].
The Chan rearrangement was effectively used to build up the furanoid structure on the way to
taxol [123,124] ( > Scheme 34).
In the syntheses of staurosporin congeners, ring-contraction reactions have been used effectively [125,126]. Novel stereoselective Beckmann-type rearrangement of TAN-1030A 147
produces the K-252 analog 148 via a hypothetical hemiacetal intermediate [127]. Oxidation of
the model compound 149, the staurosporin analog, results in ring contractive benzilic acid rearrangement to give a furanoid 150 possessing the framework of K252a [128] ( > Scheme 35).
2
General Synthetic Methods
⊡ Scheme 31
⊡ Scheme 32
been found in the fluorination reaction of the thiosugar furanose 138 [119]. It is known that
the sulfur(IV) fluoride/hydrogen fluoride system also promotes such ring-contraction reactions [120]. On Friedel–Craft reaction of the thiopentosyl bromide 140, a ring-contraction
process occurs [121]. The per-O-alkylated glycoside 142 is converted into the δ-lactone 143
with concomitant ring-contraction to furnish product 144 [122].
The Chan rearrangement was effectively used to build up the furanoid structure on the way to
taxol [123,124] ( > Scheme 34).
In the syntheses of staurosporin congeners, ring-contraction reactions have been used effectively [125,126]. Novel stereoselective Beckmann-type rearrangement of TAN-1030A 147
produces the K-252 analog 148 via a hypothetical hemiacetal intermediate [127]. Oxidation of
the model compound 149, the staurosporin analog, results in ring contractive benzilic acid rearrangement to give a furanoid 150 possessing the framework of K252a [128] ( > Scheme 35).