1.3- Dithiane-2-carboxylic acids

The dibromobutene 149 could be monosubstituted using 2-lithio-l,3-dithiane as a carboxylic acid precursor, followed by substitution of the remaining bromide with sodium azide as the amine precursor (Scheme 32). The azide was reduce under Staudinger conditions and acy-lated. After separation of the EIZ isomers, further functional group transformations gave the dimethyl-substituted Gly-Gly alkene isostere 152J123 ... 

A further safety-catch linker is based on a difhiane-protected benzoin (173). It can be activated for cleavage by photolysis according to Scheme 79, after removal of the dithiane protection [194]. It can be applied to the attachment and subsequent release of alcohols and carboxylic acids. A disadvantage is that if activation is performed with a Hg(II) salt, then this must be removed completely in order to avoid problems in assays using proteins as biological targets. 

Anions of type (4), for example (7), react with carbon dioxide at —70° to give 1,3-dithianes of a-keto carboxylic acids (11) in 70-75% yield. The reaction of carboxylic acid derivatives is more complex, but the reaction with nitriles to give 1,3-dithianes of 1,2-diketones such as (12) usually proceeds without complication.4... 

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