Ruthenium-catalysed atom-transfer cyclisation of N-(cyclohex-2-enyl)-α-chloro-α-(phenylthio)acetamides. A formal total synthesis of (±)-haemanthidine and (±)-pretazettine

The hydroindole (18), which previously served as a key intemediate in the total synthesis of (±)-haemanthidine (2) and (±)-pretazettine (1), has been prepared in a highly stereocontrolled manner by a reaction sequence involving a ruthenium-catalysed atom-transfer cyclisation of an α-chloro sulphide.