Eschenmoser sulfide contraction

The Eschenmoser sulfide contraction is an organic reaction first described by Albert Eschenmoser for the synthesis of 1,3-dicarbonyl compounds from a thioester. The method requires a base and a tertiary phosphine. The method is of some relevance to organic chemistry and has been notably applied in the vitamin B12 total synthesis.


 * Eschenmoser sulfur contraction.svg

A base abstracts the labile hydrogen atom in the thioester, a sulfide anion is formed through an episulfide intermediate which is removed by the phosphine.


 * Eschenmoser sulfur contraction mechanism.svg

Scope
The Eschenmoser sulfide contraction method has been employed in a number of total synthesis efforts, like that of fuligocandin A and B, cocaine, diplodialide A and isoretronecanol

An example of general synthetic utility is the synthesis of novel carbapenems


 * Eschenmoser sulfur contraction sakurai 1994.svg