ABSTRACT
The methods have been classified according to the type of compounds they can form (Scheme 1); for example, sugars with an heteroatom (type[), with an hydrogen (type If), or
Type I X=O,N
Type IV
Type II
Scheme 1
TypeV
with a double bond at the branching point (type Ill). Some achievements in the formation of either geminal (type IV) or vicinal (type V) doubly branched-chain sugars have been reported and will be discussed in the last section.
