A short diastereoselective synthesis of cis-(2S,4S) and cis-(2R,4R)-4-hydroxyprolines.

A concise synthesis of (2 R ,4 R )-4-hydroxyproline ( 1 ) and (2 S ,4 S )-4-hydroxyproline ( 2 ) has been developed in enantiomerically pure form from commercially available starting materials with excellent diastereoselectivity. The tightly bound chelation controlled transition state formed during the 5- exo - tet ring closure reaction is assumed to be the origin of high diastereoselectivity. [ABSTRACT FROM AUTHOR]