2.4 General Principles of Diastereoselective Reactions: Acyclic Control of Diastereoselectivity

Abstract

Diastereselectivity pertains to the relative configuration at two newly generated stereogenic centers or at a newly generated stereocenter with respect to resident stereocenters in the substrate. Diastereoselectivity arises by asymmetric induction between two emerging stereogenic centers or between resident stereogenic centers and an emerging one. Asymmetric induction occurs by steric and electronic interactions of the substituents at an inducing stereogenic center with the incoming reagent reacting at the prochiral reaction center. High diastereoselectivity requires defined spatial interactions. Hence, the conformation at all bonds connecting the inducing stereogenic center with the prochiral reaction center has to be controlled. Conformation control is thus the key to achieve high diastereoselectivity. This is more or less readily attained on cyclic substrate structures. However, it requires a special focus on open-chain substrates. Various methods such as dipole/dipole interaction, chelation, or avoidance of allylic strain have been applied to attain high diastereoselectivity in reactions of open-chain substrates.