Isopropylidene ketals carbohydrates

Cyclic ketals by transacetalation 0,0 Isopropylidene derivatives of carbohydrates with acetone dimethyl ketal... 

When a carbohydrate reacts with a vinyl ether such as 2-methoxy-l-propene, the product is a ketal. The reaction of a-d-glucopyranose (71) with this vinyl ether in the presence of an acid catalyst leads to 85. This reaction essentially protects the C4- and C6-OH units as a 1,3-dioxane (see Chapter 18, Section 18.6.6). (Protecting groups were introduced in Chapter 25, Section 25.4.3.) The name of 102 reflects the presence of this ketal it is 4,6-0-isopropylidene-a-d-glucopyranose. The isopropylidene group is the CMe2 unit, and the 0-isopropylidene name refers to the presence of the acetone ketal unit. When 71 reacts with acetaldehyde in the presence of an acid catalyst, the product is 4,6-0-ethylidene-a-d-glucopyranose, 86. The ethylidene term refers to the CHEt unit and benzylidene refers to the CHPh unit. 

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