Thioacetal

Thioacetals are the sulfur analogue of acetals. They are prepared in a similar way to acetals: by reacting a thiol with an aldehyde:
 * RSH + R'CHO &rarr;  R'CH(OH)SR

Dithioacetals are prepared similarly to thioacetals, which are intermediates:
 * RSH + R'CH(OH)SR &rarr;  R'CH(SR)2  +  H2O

Such reactions typically employ either a Lewis or Brønsted acid catalyst.

Dithioacetals generated from aldehydes and 1,2-ethanedithiol are useful in organic synthesis:
 * C2H4(SH)2 + R'CHO &rarr;  R'CHS2C2H4  +  H2O

Whereas the carbonyl carbon of an aldehyde is electrophilic, the deprotonated derivatives of dithioacetals feature nucleophilic carbon centers:


 * R'CHS2C2H4 + R2NLi &rarr;  R'CLiS2C2H4 +  R2NH

Again, this reactivity is most commonly exploited in the 1,3-dithiolanes. The inversion of polarity between R'(H)C&delta;+O&delta;- and R'CLi(SR)2 is referred to as umpolung.