dithianes

Dithianes are a class of organosulfur compounds defined by a six-membered thioacetal ring in which two sulfur atoms occupy positions 1 and 3. The canonical member is 1,3-dithiane, a ring composed of two sulfur atoms flanking four carbon atoms (S-CH2-CH2-S-CH2-CH2-). They are typically prepared by condensation of an aldehyde or ketone with 1,3-propanedithiol under acid catalysis, yielding a cyclic thioacetal that protects the carbonyl group.

The primary value of dithianes lies in their function as carbonyl protecting groups in multistep organic synthesis. The dithiane ring masks the reactivity of aldehydes and ketones, allowing otherwise problematic transformations to proceed without interference. Substituted dithianes can be formed from a broad range of carbonyl substrates, preserving the protecting group during subsequent reactions.

A key application is the Corey–Seebach umpolung chemistry. Deprotonation at the C-2 position of a dithiane with strong base generates a nucleophilic carbanion equivalent that can be alkylated or otherwise trapped with electrophiles. After the desired modifications, oxidative desulfurization or related desulfurization methods remove the dithiane, regenerating the carbonyl functionality and delivering the target product.

Desulfurization methods vary, including oxidative procedures and catalytic hydrogenolysis (for example, using Raney nickel) or other reagents that cleave the C–S bonds. The choice of method depends on the substrate and the presence of sensitive functionalities.

In summary, dithianes, especially 1,3-dithiane, serve as versatile carbonyl protecting groups and as key reagents in carbonyl umpolung strategies, enabling complex molecule construction with controlled reactivity.