C=C Bond Formation
2.6
361
⊡ Scheme 28
⊡ Scheme 29
Alternatively, the anion generated from the acetylene 56 reacted with sugar aldehydes providing two isomeric higher sugar propargylic alcohols, which were reduced (H 2 /Lindlar catalyst)
into the Z-olefins 59 ( > Scheme 27) [58].
Other methods for coupling of monosaccharide sub-units leading finally to unsaturated higher
sugars are also used, as for example the Henry reaction applied by Suami in his marvelous
synthesis of tunicamine ( > Scheme 28) [60].
Another interesting example consists of application of reactive (but at the same time stable) stannyl derivatives. Marshall prepared unsaturated precursors of dodecoses according to
> Scheme 29 [61].
The synthesis was initiated from the easily available unsaturated aldehyde 60, which reacted with tributyltin cuprate affording a 1,4-adduct (as a mixture of stereoisomers), trapped as
trimethylsilyl ethers 61a and 61b. Reaction of these reactive species with synthon 62 afforded
the unsaturated precursors of higher carbon sugars 63 and 64.
4.1 5,6-Unsaturated Pyranosides (and 4,5-Unsaturated Furanosides)
This class of compounds needs special interest. Such derivatives are especially important,
since they serve as extremely useful intermediates in the preparation of a wide variety of
carbocyclic compounds with strong biological activity (e. g. inositols, carbasugars, etc.) [5,62].
2.6
361
⊡ Scheme 28
⊡ Scheme 29
Alternatively, the anion generated from the acetylene 56 reacted with sugar aldehydes providing two isomeric higher sugar propargylic alcohols, which were reduced (H 2 /Lindlar catalyst)
into the Z-olefins 59 ( > Scheme 27) [58].
Other methods for coupling of monosaccharide sub-units leading finally to unsaturated higher
sugars are also used, as for example the Henry reaction applied by Suami in his marvelous
synthesis of tunicamine ( > Scheme 28) [60].
Another interesting example consists of application of reactive (but at the same time stable) stannyl derivatives. Marshall prepared unsaturated precursors of dodecoses according to
> Scheme 29 [61].
The synthesis was initiated from the easily available unsaturated aldehyde 60, which reacted with tributyltin cuprate affording a 1,4-adduct (as a mixture of stereoisomers), trapped as
trimethylsilyl ethers 61a and 61b. Reaction of these reactive species with synthon 62 afforded
the unsaturated precursors of higher carbon sugars 63 and 64.
4.1 5,6-Unsaturated Pyranosides (and 4,5-Unsaturated Furanosides)
This class of compounds needs special interest. Such derivatives are especially important,
since they serve as extremely useful intermediates in the preparation of a wide variety of
carbocyclic compounds with strong biological activity (e. g. inositols, carbasugars, etc.) [5,62].