Chapter 16 - Chiral Syntheses

Abstract

The chiral pool has provided the backbone of many products. Carbohydrates and amino acids are often used because of the high degree of functionality and the ready availability of these compounds from natural sources. Resolution of compounds that crystallize as true racemates requires the use of chiral adjuvants. Generally chiral amines or acids are used to separate compounds by crystallization of the diastereomeric salts. Yields are important, but minimizing the number of steps can have greater impact than increasing yields on a multistep route. This is particularly true for multistep routes on scale, where the cumulative risk and impact of processing problems increase. High-molecular-weight auxiliaries for asymmetric induction may prove less economical than a resolution. Recovery and recycling of auxiliaries will be important for minimizing long-term costs. Resolutions are most economically placed early in a synthetic sequence unless a dynamic resolution is used to increase the yield of the step.