Green chemistry and asymmetric catalysis: putting numbers on a synthesis

$$\text{AE} = \dfrac{M(\text{desired product})}{\sum M(\text{reactants})} \times 100$$ with the stoichiometric coefficients. It is read from the equation, before any experiment: $100\ \%$ for an addition or a rearrangement, less as soon as there is a co-product. It is the second of the twelve principles of green chemistry (Anastas and Warner, 1998).