Tiglic acid demercuration

In the case of mercurated tiglic acid adducts (12), the erythro product is obtained with aqueous Na2S, and an ionic mechanism has been proposed with an intermediate carboxylate enolate (25). Sodium tri-thiocarbonate and, especially, 1,3-propanedithiol exhibit a preference for retention of configuration leading to the erythro isomer. Such sulfur-containing reagents are probably capable of intramolecular hydrogen atom delivery as illustrated schematically in (26), and they also promote demercuration by an ionic mechanism. 

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