1. Sulfur-based nucleophile pKa value < 15 (DMSO) is directly connected to the nucleophile decision boundary dC-S < 1.83. 2. The electrophile protonation site must conjugate to the ipso site of reactivity. This site must also be part of the protonated heterocycle. 3. Weak acids/bases can be used in excess, but equivalents of strong acid or base must be limited to prevent inhibition of proton transfer between the substrates. 4. Polar aprotic solvents give increased relative rate, and solvent selection can be used to improve conversion and selectivity. 5. Halogen identity is generally unimportant but can be optimized to improve conversion and selectivity.