Morin rearrangement

What is Morin rearrangement?

The Morin rearrangement, also known as the Morin reaction or Morin process, is an acid-promoted stereospecific conversion of penicillin sulfoxides into corresponding desacetoxycephalosporins. It was first reported by Morin et al. in 1963 (Morin at the Lilly Research Laboratories).

Morin rearrangement - general reaction scheme
Morin rearrangement (see list of acronyms)

This rearrangement involves multiple steps including activation of sulfoxide by an acid, generation of azetidinone sulfenic acid via stereospecifically sigmatropic opening of the thiazolidine ring, protonation of sulfenic acid, and cyclization of protonated sulfenic acid with the adjacent π-bond followed by final deprotonation.

Morin rearrangement has been found to be applicable to penicillin and hetacillin sulfoxides and provides a direct chemical correlation between the penicillins and cephalosporins. The reaction has also provided a practical method for preparing important antibiotics containing deacetoxycephalosporin moiety.

Evidence for the protonation of sulfenic acid and the capture of putative cationic intermediate by carbon nucleophiles have been demonstrated. Morin rearrangement has also shown the existence of a thermal equilibrium between the sulfoxide and sulfenic acid.

References

Chemistry of Cephalosporin Antibiotics. III. Chemical Correlation of Penicillin and Cephalosporin Antibiotics
Robert B. Morin, Bill G. Jackson, Richard A. Mueller, E. R. Lavagnino, William B. Scanlon, and Sandra L. Andrews
Journal of the American Chemical Society 1963 85 (12), 1896-1897
DOI: 10.1021/ja00895a063

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