A practical synthesis of a [2.2.1] bicyclic chiral sulfide for asymmetric transformations

A substantially improved synthesis of synthetically useful chiral sulfide 1 is described. Starting from (+)-10-camphorsulfonic acid, the chiral sulfide was synthesised on large scale in five steps and 56% overall yield. Significant improvements include the use of Bu₃P in place of Ph₃P for the reduction of the chlorosulfonyl group to the thiol, allowing removal of phosphine oxide by aqueous extraction and improvements in the photochemistry using either a modified batch reactor or a single pass continuous flow reactor.