Chiral three-carbon synthons

These adverse conditions have elicited considerable efforts to reduce the number of chiral centers as well as hydroxyl groups with the simultaneous introduction of useful functional groups (10, 13-15). One approach involves the shortening of the aldose carbon chain, or, more simply, its bisection, as exemplified by the use of D-mannitol-derived 2,3-Oisopropylidene-D-glyceraldehyde. Whilst this product and its L-ascorbic acid-derived enantiomer have developed into popular enantiopure three-carbon synthons (16), it may be objected that the photosynthetic achievement of Nature which graciously provides us with six-carbon compounds, is utilized rather inefficiently, clearly pointing towards elaboration of synthons from sugars with retention of the carbon chain. 

General Three Carbon Chiral Synthons from Carbohydrates Chiral Pool and Chiral Auxiliary Approaches... 

The formation of (153) rather than (151) indicated that the estabUsh-ment of correct stereochemistries at three centres (C-2, C-3, C-4) of the synthon (149) was not sufficient to ensure the stereochemistry at C-4 a of tetrodotoxin. Probably creation of the latter as a fourth chiral centre at C-5 of the carbohydrate synthon would be advantageous, and if the carbons attached to this centre were of vastly different acidities as in (157) the course of cyclisation would be controllable. 

---