278
2
General Synthetic Methods
⊡ Figure 4
Examples of keto-anhydrosugars prepared from 1,6-anhydroglucose
⊡ Scheme 8
position inducing a cascade process leading finally to 2,3-unsaturated anhydrosugar 16 with
a nucleophile placed at the C-2 position [18].
The alternative compound 17, with the nucleophile placed at the C-4 position, was prepared by
the same method [19] from regioisomeric (to Cerny epoxide) oxirane 18, which was obtained
from D-glucal by iodocyclization followed by standard reactions ( > Scheme 7).
Many useful building blocks (besides those already presented) with preservation of the
1,6-anhydro skeleton such as levoglucosenone and its regioisomer iso-levoglucosenone can
be prepared from 1,6-anhydroglucose [20]. The carbonyl group can be also introduced at the
C-3 position by oxidation of the 2,4-diO-tosyl-1,6-anhydroglucose (12) [3] ( > Fig. 4).
Besides the reactions involving the oxygen atoms, other processes directed to functionalization
of the carbon skeleton are known. One of the most useful strategies is based on bromination of
the C-6 position and further replacement of the bromine atom with a functional group under
the radical conditions ( > Scheme 8) [21].
2
General Synthetic Methods
⊡ Figure 4
Examples of keto-anhydrosugars prepared from 1,6-anhydroglucose
⊡ Scheme 8
position inducing a cascade process leading finally to 2,3-unsaturated anhydrosugar 16 with
a nucleophile placed at the C-2 position [18].
The alternative compound 17, with the nucleophile placed at the C-4 position, was prepared by
the same method [19] from regioisomeric (to Cerny epoxide) oxirane 18, which was obtained
from D-glucal by iodocyclization followed by standard reactions ( > Scheme 7).
Many useful building blocks (besides those already presented) with preservation of the
1,6-anhydro skeleton such as levoglucosenone and its regioisomer iso-levoglucosenone can
be prepared from 1,6-anhydroglucose [20]. The carbonyl group can be also introduced at the
C-3 position by oxidation of the 2,4-diO-tosyl-1,6-anhydroglucose (12) [3] ( > Fig. 4).
Besides the reactions involving the oxygen atoms, other processes directed to functionalization
of the carbon skeleton are known. One of the most useful strategies is based on bromination of
the C-6 position and further replacement of the bromine atom with a functional group under
the radical conditions ( > Scheme 8) [21].