Table : Some of the experimentally measured ratio of regisomers (α/β) that support two alternative pathways. The reaction is shown in Figure for different additives, Pd-ligands, and X ( a indicates that I is used in instead of Br). X (PPh 3 ) 2 DPPP DPPP + Ag + /Tl + Br 76/24 a 61/39 >99/1 OTf 63/37 >99/1 -To sum up, the main difference for α vs β selectivity is the much higher percentage of bidentate ligands (93 % vs 4 %, respectively) when α is observed, although early work by Cabri suggests that this alone does not result in α selectivity (Table ). Another difference between the α and β set is the alkene substituent. For the α set, in 91 % of the cases the atom bonded to the alkene is either O or N or an aliphatic C bonded to O or N, while for the β set 75 % of the corresponding atoms are either a carbonyl (mostly esters) or an aromatic carbon (Table Calculations for the neutral and cationic pathways are on the top and bottom, respectively.