254
2
General Synthetic Methods
⊡ Scheme 53
3.3.2 Addition to Isolated Alkenes
The p-toluenesulfonylimidoosmium reagent, which may be generated from Chloramine-T and
osmium tetraoxide, leads to cis-addition of OH and HNTs to the least-hindered face of double
bonds. With the hex-2-enopyranoside 97, the addition occurs to the top face of the double bond
to give the regioisomers 109 and 110 ( > Scheme 54) [92].
Vinyl sulfone-modified carbohydrates, such as 111, can be subjected to Michael addition reaction with primary or secondary amines to construct 112 bearing amino groups at the C-2 carbon
in equatorial configurations ( > Scheme 55) [93].
An 1-hydroxy-1,2-benziodoxol-3(1H)-one 1-oxide (IBX)-mediated process provides another
efficient and stereoselective preparative route for the synthesis of amino sugars. For example,
reaction of the D-glucal derivative 113 with p-methoxybenzene isocyanate in the presence of
a catalytic amount of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) followed by treatment with
IBX furnishes the cyclic carbonate 115, through urethane 114. Subsequent removal of the
p-methoxybenzyl (PMB) protecting group by CAN affords the protected amino sugar 116
( > Scheme 56) [94].
⊡ Scheme 54
⊡ Scheme 55
2
General Synthetic Methods
⊡ Scheme 53
3.3.2 Addition to Isolated Alkenes
The p-toluenesulfonylimidoosmium reagent, which may be generated from Chloramine-T and
osmium tetraoxide, leads to cis-addition of OH and HNTs to the least-hindered face of double
bonds. With the hex-2-enopyranoside 97, the addition occurs to the top face of the double bond
to give the regioisomers 109 and 110 ( > Scheme 54) [92].
Vinyl sulfone-modified carbohydrates, such as 111, can be subjected to Michael addition reaction with primary or secondary amines to construct 112 bearing amino groups at the C-2 carbon
in equatorial configurations ( > Scheme 55) [93].
An 1-hydroxy-1,2-benziodoxol-3(1H)-one 1-oxide (IBX)-mediated process provides another
efficient and stereoselective preparative route for the synthesis of amino sugars. For example,
reaction of the D-glucal derivative 113 with p-methoxybenzene isocyanate in the presence of
a catalytic amount of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) followed by treatment with
IBX furnishes the cyclic carbonate 115, through urethane 114. Subsequent removal of the
p-methoxybenzyl (PMB) protecting group by CAN affords the protected amino sugar 116
( > Scheme 56) [94].
⊡ Scheme 54
⊡ Scheme 55