Lithiodithianes acylation

Acylation with Lithiodithianes 2.4.9J Miscellaneous Reactions of Dithioacetals... 

Reaction of lithiodithianes with acyl chlorides, esters or nitriles leads to the fOTination 1,2-dicarbonyl compounds in which one of the carbonyl groups is protected as the thioacetal. d76043j44 Optically active amino ketones of type (69) are inepared via acylation of dithiane with an oxazoline-protected (5)-serine methyl ester (Scheme 41). Optically active (5)-2-alkoxy-l-(l,3-dithian-2-yl)-l-propanones were prepaid by the reaction of the corresponding methyl (5)-lactate with 2-lithio-l,3-enantioselective synthesis of (-)-trachelanthic acid. Enantioselective synthesis of L-glyceraldehyde involves the acylation of a dithiane glycolic acid derivative followed by bikers yeast mediated reduction. ... 

B.ii. Acyl Anion Equivalents. The most common umpolung equivalent is that for acyl anion 339, and dithianes 344 are the most common reagent used for this purpose. Dithiane 344 is prepared from an aldehyde, but ketones are also precursors (sec. 7.3.B.ii). Removal of the hydrogen adjacent to the sulfur requires a base such as n-butyllithium and the product is a-lithiodithiane (345). The acidity of this hydrogen is largely... 

Acylation of 2-lithio-l,3-dithiane derivatives occurs in satisfactory yields only when a dilute solution of the dithiane derivative is added at —78°C to a solution containing a 20-100-fold excess of the acylating agent (equation 62). The above conditions are necessary to circumvent reaction of a molecule of the reactive lithiodithiane with a molecule of previously formed 2-acyldithiane. This method offers, by subsequent removal of the dithioketal function, a route for the preparation of 1,2-dicarbonyl compounds. 

Acylating agents that have been employed are carbon dioxide, alkyl chloroformates, alkyl formates, add chlorides, esters, benzonitrile and dimethylformamide the expected acylation products from reaction with the above reagents were formed in each case. However, the N,N-dimethyl-amide derivatives of higher carboxylic acids did not yield acylated product as in the case of dimethylformamide . When R = H (equation 63), it was necessary to employ two equivalents of the lithiodithiane due to product enolate formation. 

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