Thermolysis of Isomigrastatin and Its Congeners via [3,3]-Sigmatropic Rearrangement:  A New Route to the Synthesis of Migrastatin and Its Analogues

Thermolysis of isomigrastatin (1) under neat heating conditions afforded migrastatin (1a). The reaction is proposed to proceed via a concerted [3,3]-sigmatropic rearrangement by which ring expansion is achieved regio- and enantiospecifically. The general applicability of this reaction was demonstrated with six additional isomigrastatin congeners (3−8), providing a new route to the synthesis of migrastatin analogues (3a−8a).