Is there stereoelectronic control in hydrolysis of cyclic guanidinium ions?
To assess stereoelectronic effects in the cleavage of tetrahedral intermediates, a series of five-, six-, and seven-membered cyclic guanidinium salts was synthesized. If stereoelectronic control by antiperiplanar lone pairs is operative, these are expected to hydrolyze with endocyclic C-N cleavage to acyclic ureas. However, hydrolysis in basic media produces mixtures of cyclic and acyclic products, as determined by 1H NMR analysis. The results show that in the six-membered ring antiperiplanar lone pairs provide a weak acceleration of the breakdown of the tetrahedral intermediate, but in five- and seven-membered rings there is no evidence for such acceleration, which instead can be provided by syn lone pairs.
Perrin
C L
CL
Department of Chemistry, University of California, San Diego, La Jolla, California 92093-0358, USA.
Young
D B
DB
D019791:Guanidine / Q000737:chemistry*; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D013237:Stereoisomerism; D014508:Urea / Q000737:chemistry
D014508:Urea; D019791:Guanidine