Spiro compounds spiroketals

Acetals such as C are referred to as spiroketals because their acetal carbon is a spiro atom. (In a spiro compound two rings are connected by a single common atom that is called a spiro atom ). The intermediates in this acetalization are lactols B. They resemble those lac-tols whose rapid formation from y- or 5-hydroxyketones was shown in Figure 9.4. Note that because of the unfavorable reaction entropy, there is often no path hack from spiroketals to the open-chain form Usually, spiroketals cannot be hydrolyzed completely. 

Spiroacetals (spiroketals). A widely distributed class of natural products with characteristic structural features intramolecular ring closure of a dihydroxy ketone furnishes a bicycUc compound in which one carbon atom (that of the original carbonyl group) is shared by both rings. This so-called spiro center is bound to one carbon atom and one oxygen atom in both rings. 

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