ORGN 297 |
Mild lanthanide(III)-promoted formation of 4,5-diaminocyclopent-2-enones from 2-furaldehyde and secondary amines
| Sze Wan Li and Robert A. Batey. Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON M5S 3H6, Canada |
| The synthesis of novel diamines has attracted considerable interest, not only as scaffolds for combinatorial library generation, but also due to their potential to act as ligands for metal ions. The 1,2-diaminocyclopentane core structure is one such general scaffold, which has been relatively under-explored due to difficulties in its synthesis. Here we describe the first example of the preparation of 4,5-diaminocyclopent-2-enones 1 by the Lewis acid catalyzed reaction of 2-furaldehyde and secondary amines. The use of lanthanide triflates as Lewis acid catalysts allows the facile one-pot synthesis of richly functionalized cyclopentenones with exclusive control of diastereochemistry and in excellent yields. A computational study revealed that the highly diastereoselective nature of this transformation was due to a thermal conrotatory Ĉ4a electrocyclization of a ring-opened intermediate (a deprotonated Stenhouse salt). A kinetic study on the ring closure of the aniline derived Stenhouse salt, revealed the reaction to occur with an activation barrier of 16.3 kcal/mol. 
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