α-Iodo-α,β-Unsaturated Ketones as Vicinal Dielectrophiles: Their Reactions with Dinucleophiles Provide New Annulation Protocols for the Formation of Carbo- and Heterocyclic Ring Systems

Advances in the Synthesis of Cyclopropylamines

Cyclopropylamines are an important subclass of substituted cyclopropanes that combine the unique electronic and steric properties of cyclopropanes with the presence of a donor nitrogen atom. In addition to their presence in a diverse array of biologically active compounds, cyclopropylamines are utilized as important synthetic intermediates, particularly in ring-opening or cycloaddition reactions. Consequently, the synthesis of these compounds has constituted a significant research topic, as evidenced by the abundant published synthetic methods. In addition to the widely used Curtius rearrangement, classical cyclopropanation methods have been adapted to integrate a nitrogen function (Simmons-Smith reaction, metal-catalyzed reaction of diazo compounds on olefins, Michael-initiated ring-closure reactions) with significant advances in enantioselective synthesis. More recently, specific methods have been developed for the preparation of the aminocyclopropane moiety (Kulinkovich reactions applied to amides and nitriles, addition to cyclopropenes, metal-catalyzed reactions involving C-H functionalization, ...). The topic of this review is to present the different methods for the preparation of cyclopropylamine derivatives, with the aim of covering the methodological advances as best as possible, highlighting their scope, their stereochemical aspects and future trends.

A General Method to Access Underexplored Ylideneamino Sulfates as Interrupted Beckmann-Type Rearrangement Intermediates

The Beckmann rearrangement of ketoximes to their corresponding amides, using a Brønsted acid-mediated fragmentation and migration sequence, has found wide-spread industrial application. We postulated that the development of a methodology to access ylideneamino sulfates using tributylsulfoammonium betaine (TBSAB) would afford isolable Beckmann-type intermediates and competent partners for subsequent rearrangement cascades. The ylideneamino sulfates generated, isolated as their tributylammonium salts, are sufficiently activated to undergo Beckmann rearrangement without additional reagent activation. The generation of sulfuric acid in situ from the ylideneamino sulfate giving rise to a routine Beckmann rearrangement and additional amide bond cleavage to the corresponding aniline was detrimental to reaction success. The screening of bases revealed inexpensive sodium bicarbonate to be an effective additive to prevent classic Brønsted acid-mediated fragmentation and achieve optimal conversions of up to 99%.