Ketal, cyclopentylidene

The cyclopentylidene ketal has also been prepared from dimethoxycyclopen-tane, TsOH, CH3CN, and can be cleaved with 2 1 ACOH/H2O, rt, 2 h. ° Meth-oxycyclopentene (PPTS, CH2CI2, rt, 100%) has also been used to introduce this group." ... 

Cyclopentylidene Ketal, i Cyclohexylidene Ketal, ii Cycloheptylidene Ketal, iii... 

R. Csuk and B. I. Glanzer, Synthetic usefulness of the sugar cyclopentylidene ketals, J. Carbohydr. Chem., 9 (1990) 809-822. 

The 1,3-anti -reduction of (3-hydroxy ketones was utilized in the total synthesis of (+)-roxaticin (14), a pentaene macrolide isolated from streptomycete X-149944 (Scheme 4.2e). The (3-hydroxy ketone 15 underwent 1,3-anti -reduction to afford the diol 16 in 99% yield and greater than 95 5 diastereoselectivity. The resulting diol was then protected as a cyclopentylidene ketal (17) by using cyclopentylidene dimethyl ketal and pyridinium p-toluene sulfonate (PPTS). 

Other ketals which are frequently used if a modified acid stability is wanted are the cyclopentylidene, the cyclohexylidene and the cycloheptylidene ketals. They are readily prepared by the reaction of a diol and the cycloalkanone in toe presence of ethyl orthoformate and mesitylenesulfonic acid. The relative rates of their acid-catalyzed hydrolysis are given in Scheme 50. 

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