Formyl anions, synthons

The Michael addition of nitromethane to cyclopentenone derivatives is used for synthesis of prostaglandins (Scheme 4.20).158 Here, the anion of nitromethane is used as a formyl anion synthon. 

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. 

Aldehyde synthesis. Aldehydes are obtained through alkylation under solid-liquid biphasic conditions followed by reduction with LiAlH4 and Hg(II)-promoted hydrolysis. Thus the bissulfonyl methanes are a formyl anion synthon. 

Hence, (1) serves as a synthetic equivalent for the formyl anion synthon which adds to the aldehyde in a stereoselective manner, creating a new chiral hydroxymethylene center. The repetition of the first and second operational sequences above over six consecutive cycles with high levels of diastereoselectivity and chemical yields in each cycle provided a series of protected D-aldoses having up to nine carbons in the chain (eq 8). 

Two groups have reported the use of phenylthiomethyltrimethylsilane as a formyl anion synthon. Alkylation of the lithium anion may be accomplished in THF, or in hexane containing TMEDA. A distinct advantage of this formyl synthon is the ease of unmasking the aldehyde via a sila-Pummerer rearrangement (Scheme 6). However, as steric crowding about the intermediate sulphoxide... 

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