Synthesis of (2R,5R)-2-Amino-5-Hydroxyhexanoic Acid by Intramolecular Cycloaddition

The title compound was synthesized from sorbic acid by an eight step sequence. The key step was the stereospecific intramolecular Diels-Alder reaction of the acylnitroso derivative of N-sorbyl-L-proline (5). L-Proline served as a temporary tether which directed both the stereochemistry and the regiochemistry of the cycloaddition.