Applications of Intramolecular Cyclopropanations of Chiral Secondary Allylic Diazoacetates

Abstract

The diastereomeric secondary allylic diazoacetates 6a,b and 8a,b, which were readily prepared from the common intermediate 4, were cyclized in the presence of the achiral catalyst Cu(TBS)2 to furnish mixtures of the adducts 9a,b/10a,b and 12a,b/13a,b, respectively; in these cyclizations, the diastereoselectivity of the reaction was substrate controlled. When 6a,b and 8a,b were cyclized in the presence of the chiral catalysts Rh2[(5S)-MEPY]4 or Rh2[(5R)-MEPY]4, the substrate-based selectivity could be reversed if the chirality of the substrate and catalyst were matched. The advantages associated with the use of chiral catalysts to effect the diastereoselective cyclization of chiral allylic diazoacetates were demonstrated by the synthesis of 25, which comprises the cyclopropane subunit found in the diterpene ingol B (14).