Dithiane anions formation from aldehydes

In particular, 1,3-dithiane prepared from dimethoxymethane (methylal) and pro pane-1,3-dithiol in the presence of boron trifluoride-etherate,237 and 2-alkyl-1,3-dithianes prepared similarly from aldehydes,2383 are important acyl anion equivalents. These and other uses are discussed in Sections 5.7.5, p. 596, and 6.6.1, p. 909. A wide-ranging review of the reversal of polarity of the carbonyl group through the formation of these sulphur-containing reagents has emphasised their value in organic synthesis.2388... 

Protection of 194 as a p-methoxybenzylether and subsequent epoxydation led to the trans-epoxide 195, which was transformed into the unsaturated aldehyde 196 by a three-reaction sequence, including regioselective oxirane opening with a 1,3-dithiane anion, hydrolysis of the dithioacetal formed, and dehydration. Chlorite promoted aldehyde oxidation, methyl ester formation, and removal of the hydroxyl protections delivered methyl (+)-shikimate 197 in a remarkable 12% yield from 193. 

Aggarwal has discovered that the anion derived from 1,3-dithiane dioxide undergoes rapid reaction with a range of aldehydes leading to the formation of diastereoisomeric mixtures in good yield (Scheme 20).76b... 

The 1,3-dithiane anion can be prepared in two steps from the corresponding aldehyde (formation of thioacetal, followed by deprotonation). Another option is to start with formaldehyde. Alkylation of its 1,3-dithiane anion will introduce the required ethyl group. This method can be used to prepare a variety of 13-dithiane compounds, and can even be used to synthesize aldehydes and ketones (one or two alkylation steps, followed by hydrolysis). 

Acylsilanes. The reaction of anion (1) with alkyl halides generates a functionalized dithiane which, when hydrolyzed under mild conditions, provides the corresponding acylsilane (eq 16). More highly substituted acylsilanes have been accessed by initial formation of the dithiane from the aldehyde, followed by deprotonation and silylation with TMSCl (eq 17). Acylsilanes have been used as sterically hindered aldehyde equivalents forre-giocontrol in addition reactions (eq 18) and also as precursors for silyl-substituted vinyl triflates (eq 19). ... 

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