Site-Selective, Catalyst-Controlled Alkene Aziridination

Abstract

Transition-metal-catalyzed nitrene transfer is a convenient method to introduce nitrogen into simple substrates through either alkene aziridination or C–H bond amination. Silver complexes have an unusual capability to accommodate a broad range of N-donor ligands and coordination geometries in catalysts competent for nitrene transfer. This behavior has resulted in the ability to achieve tunable chemoselectivity between aziridination and C–H bond amidation, as well as tunable site-selective functionalization between two different C–H bonds. In this paper, efforts to engage the diversity of silver and rhodium catalysts to accomplish selective and tunable aziridination of mixtures of alkenes are discussed. It was found that the selectivity of dinuclear Rh catalysts is dictated largely by steric effects, while the identity of the ligand on silver can be tuned to influence whether the steric or electronic features in the competing alkenes is the primary factor controlling which precursor is preferentially aziridinated.

Cationic Divalent Metal Sites (M = Mn, Fe, Co) Operating as Both Nitrene-Transfer Agents and Lewis Acids toward Mediating the Synthesis of Three- and Five-MemberedN-Heterocycles

“…Among the common synthetic methods for synthesizing aziridines (cyclization of 1,2-amino precursors, addition of C 1 sources to imines, addition of N 1 sources to olefins), the “C 2 + N 1 ” methodology has received extensive attention and can be accomplished under a variety of organocatalytic or metal-dependent conditions, usually with the assistance of middle or late first-row transition elements, − coinage metals, , and platinum-group elements. − The requisite N 1 donors are frequently sourced from a wide variety of nitrene- or nitrenoid-group (NR, NR­(X)) precursors (e.g., organic azides, iminoiodinanes, haloamines, N / O -substituted hydroxylamines, N -tosyloxycarbamates), thus providing an enormous backdrop for the synthesis of both activated (EW nitrogen substituent, e.g., −SO 2 R, −CO 2 R, −C­(O)­R) and nonactivated aziridines (ED nitrogen substituent, e.g., H, alkyl, aryl, silyl) …”

Iodonium imides in organic synthesis

“…Schomaker's group utilized intramolecular aziridination reactions of appropriate amide precursors and PhIO in the presence of transition metal catalysts in numerous syntheses of stereochemically complex products. 150,151 For example, intramolecular aziridination of homoallenic sulfamates 53 (Scheme 20) using a dinuclear Rh(II) catalyst, such as Rh 2 (TPA) 4 (TPA = triphenylacetate), yielded exocyclic methyleneaziridines 54 with excellent chemo-, regio-, and stereoselectivity. 150,152 This aziridination was followed by immediate ringopening of the initially formed labile intermediate 54 to afford enesulfamates 55 in good yield and excellent stereoselectivity in favor of the E isomer.…”

A Comparative Study of Cationic Copper(I) Reagents Supported by Bipodal Tetramethylguanidinyl-Containing Ligands as Nitrene-Transfer Catalysts

“…Among three commonly employed synthetic strategies (cyclization of 1,2-amino precursors, addition of C 1 sources to imines, addition of N 1 sources to olefins), the N 1 +C 2 methodology is used more frequently than others by means of organocatalytic and metal-dependent reagents, the latter employing middle or late first-row transition-metal elements, − coinage metals, , and platinum-group elements. − Issues of selectivity (chemo, regio, stereo, or enantio) have been addressed by using suitably developed supporting frameworks, such as porphyrinoid, C 2 -symmetric chiral salen, and bis­(oxazoline) ligands, as well as by virtue of the more recently developed genetically engineered hemeproteins . The nitrene moiety (NR) transferred with the assistance of these reagents to olefinic substrates or C–H bonds is sourced from a variety of nitrene or nitrenoid precursor groups (NR, NR­(X)), most commonly by means of iminoiodinanes, organic azides, haloamines, N/O-substituted hydroxyl amines, and N-tosyl carbamates …”

“…Among three commonly employed synthetic strategies (cyclization of 1,2-amino precursors, addition of C 1 sources to imines, addition of N 1 sources to olefins), 14 the N 1 +C 2 methodology is used more frequently than others by means of organocatalytic and metal-dependent reagents, the latter employing middle or late first-row transition-metal elements, 15 − 20 coinage metals, 21 , 22 and platinum-group elements. 23 − 25 Issues of selectivity (chemo, regio, stereo, or enantio) have been addressed by using suitably developed supporting frameworks, such as porphyrinoid, C 2 -symmetric chiral salen, and bis(oxazoline) ligands, as well as by virtue of the more recently developed genetically engineered hemeproteins.…”