Grob Fragmentation

C. A. Grob, W. Baumann, Helv. Chim. Acta 38, 594 (1955).

Carbon-carbon bond cleavage primarily via a concerted process involving a five atom system:

The intramolecular version is useful for the preparation of medium-size rings:

M. Ochiai et al., J. Org. Chem. 54, 4832 (1989); S. Nagumo et al., Tetrahedron 49, 10501 (1993); J.-J. Wang et al. ibid. 54, 13149 (1998). Synthetic applications: S. Schreiber, J. Am. Chem. Soc. 102, 6163 (1980); J. Boivin et al., Tetrahedron Letters 40, 9239 (1999); A. Krief et al., ibid. 41, 3871 (2000). Reviews: C. A. Grob, Angew. Chem. Int. Ed. 8, 535-546 (1969); P. Weyerstahl, H. Marschall, Comp. Org. Syn. 6, 1044-1065 (1991). Cf. Eschenmoser Fragmentation; Wharton Reaction.