Unusual ring opening of a Cyclopropylideneamine derivative during a favorskii-type rearrangement of α-Chloroketimines

The Favorskii Rearrangement: Synthetic Applications

“…Protonation of anions I V and/or V in the hydrolysis step yields the final products. Predominance of the formation of IV or V is governed by the stability of the generated carbanions, although steric factors can also determine the direction of the ring opening of the cyclopropanone [8]. Experimental support for this mechanism was provided by Loftfield by using an isotopically labelled 2-chlorocyclohexanone as substrate [9].…”

“…The reaction of -chloro ketimines 37a (Scheme 18) with two equivalents of LDA afforded cyclic amidines 48 in good yields [8]. The proposed mechanism for this transformation involves the reaction of two molecules of the intermediate cyclopropylideneamines 4 0 a to give 4 9 .…”

1-Azaallylic Anions in Heterocyclic Chemistry

“…66 This reaction was explained as starting with a baseinduced Favorskii-type ring contraction, affording cyclopropylidenamines 121 (N-analogues of cyclopropanones), followed by a "dimerization" process involving addition of zwitterion 120 across the imino bond of the cyclopropylidenamine 121 and subsequent opening of the resulting aminal anion 122 to the most stable carbanion 123. The ring-closed isomeric species 124, i.e., cyclopropylideniminium ions in equilibrium with 123, suffered nucleophilic addition, affording spiro intermediate 125.…”

Highly Regioselective Transformation of Alkenyl Bromides into α-Bromoaziridines and α-Bromohydrazones

“…α-Halogenated imines and hydrazones have been used for the preparation of diimines, epoxyimines, cyclopropylamines, pyrrolidines, and pyrroles. 1a, However, the efficient synthesis of α-halogenated imines and hydrazones is an underdeveloped area in comparison with α-halogenated aldehydes and ketones . This is due to the difficulties encountered during the preparation of these intermediates.…”