A two-step procedure for the preparation of cyclopropanecarboxaldehyde-1,1-diester from a γ,δ-epoxyester and its synthetic versatility are described herein. The epoxide ring-opening/cyclopropanation process occurs in the presence of Mg(ClO4)2 under heating, resulting in cyclopropanemethanol-1,1-diester in 65% yield. A mild TEMPO-mediated oxidation of this substrate readily generated the corresponding aldehyde in 75% yield, which was applied in the one-pot synthesis of four cyclopropylidene γ-lactams and three δ-lactams. In addition, vinyl cyclopropanes were obtained through the Wittig reaction of the aldehyde with phosphonium salts and used as precursors for tetrahydrofurans.

A straightforward synthesis of cyclopropylidene iminolactones mediated by triflic acid under mild conditions is described. Different types of hydroxy‐substituted cyclopropanecarboxamides containing a variety of functional groups participated in this smooth cyclization through an intramolecular SN2 attack of the amidic oxygen on the protonated carbinol group with the release of water. Ten cyclopropylidene iminolactones were readily obtained in high purity after a basic work‐up with no additional chromatographic separation (62–98 % yield). Besides the simplicity, the method is highly diastereoselective and tolerates several functional groups, demonstrating the broad scope of this process. Selected iminolactones were applied in further synthetic transformations to give functionalized cyclopropanecarboxamides through hydrogenolysis or nucleophilic ring‐opening reactions.

No abstract