Acetal Selective formation under thermodynamic

The diketone shown below reacts selectively with 1 equivalent of 1,2-ethanediol to give a monoacetal. Since acetal formation is reversible, the reaction is under thermodynamic control. Use Spartan View to obtain the energies of monoacetals A and B, and predict which is favored. 

A detailed study of the formation of ( )- and (Z)-silyl ketene acetals was recently published. It was found that the formation of silyl enolates does not correspond to simple kinetic vs. thermodynamic formation of the enolates. Formation of the ester enolates occurred under kinetic control and a kinetic resolution accounted for selective formation of ( )- and ( -silyl ketene acetals. Table 3 summarizes some of these results. 

Bartlett and Hahne have achieved selective synthesis of the diastereomeric amides by the reaction of allylic alcohols and ynamine. When the reaction was carried out at ambient temperature in the presence of BF3, the ketene Af,C -acetals have the thermodynamically favored Z-configuration. If the reaction was carried out by adding the alcohols slowly to a refluxing solution of an ynamine in xylene, the rearrangement proceeded via formation of a kinetically controlled intermediate with -configuration. Thus alcohol 110 reacted with ynamine 111 using BF3 at 25 °C to give 114 and 115 in the ratio of 1 10. The product ratio was reversed (114/115 = 10 1) when the reaction was conducted under eonditions of kinetic control (Scheme 9). 

---