Cram's rule

from Wikipedia, the free encyclopedia

The Cram rule is one of Donald J. Cram established in 1952 empirical stereochemical rule. It allows a qualitative prediction of the stereochemical course of a diastereoselective nucleophilic addition of organometallic compounds to a carbon-oxygen double bond which has a chiral center with three substituents of different spatial filling in the α position .

The substituents are referred to as large, medium and small according to their space filling. A nucleophile always attacks from the side with the least steric hindrance.

Scheme 1. Cram's rule of asymmetric induction

The rule has been further developed in the Felkin-Anh rule .

Individual evidence

  1. Donald J. Cram, Fathy Ahmed Abd Elhafez: The Rule of “Steric Control of Asymmetric Induction” in the Syntheses of Acyclic Systems. In: Journal of the American Chemical Society. 74, 1952, pp. 5828-5835, doi : 10.1021 / ja01143a007 .