# Neighbouring group participation with and without retention of configuration in nucleophilic substitution of 2,6-dichloro-9-thiabicyclo[3.3.1]nonane

Treatment of the dichloride A under the conditions indicated gives B with retention of configuration, while treatment of dichloride C gives D with inversion of configuration.

I am having difficulty drawing out the inversion ring product to find out if the s lone pair can attack from anti to the $\ce{C-Cl}$ σ* bond on the vertical ring. If it does, then, there is retention of product in the first reaction after the $\ce{N3-}$ attacks.