¹³C NMR study of the structures of open‐chain bis‐reissert analogues and their salts

Abstract

The structures of open-chain bis-Reissert analogues and their salts were investigated using I3C NMR spectroscopy. Evidence is presented to show that the former exists in the acyclic form in solution. Detailed structural studies and the I3C NMR data clearly show that, in solution, the open-chain bis-Reissert salt analogues exist predominantly as the amino tautomer.

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“…However, the mechanistic pathway for the conversion bis‐oxazolium salts to the corresponding bis‐amino acid remains to be fully elucidated. Nevertheless, our results are consistent with structural studies on other classes of Reissert compounds [21–23].…”

“…The bis‐oxazolium salt exists as different tautomeric forms I–III , which could interconvert in solution. We previously reported the 13 C NMR study of the representative bis‐oxazolium perchlorate salts and confirmed that the amino form II is the most predominant tautomer in solution [21]. Our results are in agreement with that of Cook et al .…”

“…[22]. The salt was found to revert back to the Reissert compound over a period of time in the presence of DMSO [21]. The open‐chain bis‐Reissert compounds were also converted to the corresponding bis‐amino acid in the presence of 36% HCl presumably via the formation of the bis‐oxazolium salt intermediate and subsequent hydrolysis [19].…”