and 2b are all exergonic, step 3a is considerably endergonic. This suggests that once formed there is little driving force for 3 to react further and it would be expected to be a thermodynamic sink of the reaction sequence. As such it remains more likely that the pathway bifurcates at 2a and this is a common intermediate to form the double C-S activation product 3 and desulfurisation products 4 and 5.