The thiol anion produced in the reaction thus far makes a nucleophilic attack on the thiirane S atom (f + = 0.589) at the 8-and 14-positions, resulting in the formation of CAR and disulfide (BCysM) . Reacting at the second reactive 14-position (f + = 0.107) of 4, the thiirane ring is opened by the attack of the thiyl anion (RS -), and the aromaticity is restored by the elimination of one mole of the thiol to yield product 2.