text: Synthesis for a standard β-blocker begins with the mono-alkylation of catechol to give an ether (see figure 4).
  The fundamental step, and usually the last, in the synthesis of β-blockers consists of adding a propanolamine side chain. This can be done following two paths which both involve alkylation of an appropriate phenoxide with epichlorohydrin (ECH). The first way is shown as the upper way in figure 5. It consists of phenoxide reacting at the oxirane and resulting in an alkoxide, that displaces the adjacent chloride to form a new epoxide ring. The second way is shown as the lower route in figure 5. It consists of displacement of the halogen directly with a S2 reaction to give the same glycidic ether. When following both pathways, the central chiral carbon preserves its configuration, which is an important part to consider when synthesizing enantiomerically defined drugs. The ring opening of the epoxide ring in glycidic ether is done with an appropriate amine, such as isopropyl amine or tert-butylamine, and leads to the aryloxypropanolamine compound that consist of a secondary amine. This amine is typically known as the structural requirement for the β-adrenergic blocking activity.