Formyl anion synthon, reagent equivalents

Although various compounds are known to act as synthetic equivalents to the formyl anion synthon,12 the advantages that appear to be associated with the use of 2-TST warrant comment. First, 2-TST is a readily available, relatively cheap, and storable reagent second, it reacts promptly and stereoselectively with aldehydes under neutral conditions third, it gives high yields of products that are stable to isolation and purification and nevertheless can be readily transformed into aldehydes. 

The acyl anion (R-C=0) is not stable as such, but when an aldehyde is converted into a 1,3-dithiane by reaction with propane-1,3-dithiol and then treated with base, it forms an acyl anion equivalent, and hence is susceptible to attack by electrophilic reagents (see Section 5.9). Two extensive compilations of formyl and acyl anion synthons together with references to their reactions... 

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