Allose acetonation

J. Gelas and D. Horton, Kinetic acetonation of D-galactose, D-allose and D-talose with alkyl propenyl ethers as a preparative route to the 4,6- O-isoptopylidene aldohexopyranoaes, Carbohydr. Res. 77 103 (1979). 

The availability of convenient routes to many rare sugars has prompted studies on their acetalation. Often, the products had previously only been prepared indirectly. Thus, acetonation of D-allose was found to give 2,3 5,6-di-0-isopropylidene-D-allofuranose as the main product.13,14 The corresponding 1,2 5,6-diacetal is also formed, but in very low yield. Likewise, the condensation of acetaldehyde (as... 

Acetonation of D-talose in the presence of anhydrous copper(II) sulfate and sulfuric acid gave, as the major product, the 2,3 5,6-diacetal (28%) with a smaller proportion of the 1,2 5,6-diacetal (10%).16 These results are in accordance with the predictions of Mills10 that the 2,3 5,6-diacetals of mannose, gulose, allose, and talose would be thermodynamically favored, as they have the minimum number of endo substituents. 

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