For more detailed information on TS modeling for the prediction of enantioselectivity, we refer the readers to previous reviews. Calculating the stereoselectivity from the energy difference ΔΔG ‡ assumes that the reaction is under Curtin-Hammett control (Figure ). Simply put, the product ratio (e.g., R:S) reflects the energy difference between the two competing and irreversible diastereomeric TSs (i.e., ΔΔG ‡ ). Since the difference in ΔΔG ‡ between a moderately selective catalyst (~80 %ee) and an excellent catalyst (>97 %ee) is about 1 kcal/mol, there is a requirement for the methods to be accurate enough to be able to distinguish between them. Hence, a prediction error within 1 kcal/mol is targeted. While high level calculations may fulfill this criterion, an objective is to obtain predictions quicker than experimental data and using less expensive equipment. Unfortunately, the most accurate methods for modelling TSs (e.g., MP2, DFT) are demanding in both computational resources and time. It follows that they can hardly compete with high throughput experimentation which provides true data (not predictions) in a time-efficient manner. As a result, these high-level calculation methods are primarily used to investigate reactions post facto rather than for designing novel catalysts. 72 Thus, faster alternative methods are necessary.