Isopropenyl Acetate aldol reactions

N-Acetvlneuraminic Acid Aldolase. A new procedure has also been developed for the synthesis of 9-0-acetyl-N-acetylneuraminic acid using the aldolase catalyzed reaction methodology. This compound is an unusual sialic acid found in a number of tumor cells and influenza virus C glycoproteins (4 ). The aldol acceptor, 6-0-acetyl-D-mannosamine was prepared in 70% isolated yield from isopropenyl acetate and N-acetyl-D-mannosamine catalyzed by protease N from Bacillus subtilis (from Amano). The 6-0-acetyl hexose was previously prepared by a complicated chemical procedure (42.) The target molecule was obtained in 90% yield via the condensation of the 6-0-acetyl sugar and pyruvate catalyzed by NANA aldolase (Figure 6). With similar procedures applied to KDO, 2-deoxy-NANA and 2-deoxy-2-fluoro-NANA were prepared from NANA. 

Enol esters, like enol ethers, can also react with various acetals and aldehydes in the presence of Lewis acids such as TiCU, AlCb, SnCU, ZnCh, and BFs OEt to afford the corresponding aldol-type addition products. A typical example is the reaction of isopropenyl acetate and 7-phenylpropionaldehyde acetal... 

The Lewis acid-promoted reaction of benzaldehyde with isopropenyl and a-styryl acetates gives acetyl-protected aldols. This aldol reaction is effectively catalyzed by Me3Si[B(C6F5)4] [16]. 

Aldol Reactions. Isopropenyl acetate participates in some aldol-type reactions. This enol ester, like enol ethers, can react with various acetals (20) in the presence of a Lewis acid to afford the aldol-type addition products (21 and 22) (eq 10). This same reactivity is observed in the condensation of Succinic Anhydride with isopropenyl acetate. ... 

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