Abstract
The prevalence of stereochemically complex amines in natural products, pharmaceuticals and other bioactive compounds, coupled with the challenges inherent in their preparation, has inspired our work to develop new and versatile methodologies for the synthesis of amine-containing stereotriads ('triads'). The key step is a highly chemo-, regio-, and stereoselective transition-metal catalyzed nitrene transfer reaction that transforms one of the cumulated double bonds of an allene precursor into a bicyclic methyleneaziridine intermediate. This account summarizes our strategies to rapidly elaborate such intermediates into stereochemically rich, densely functionalized amine triads, nitrogen heterocycles, aminated carbocycles and other useful synthetic building blocks.
Highlights
1.1 Key features of chiral allenes enabling stereoselective syntheses of amine triads Chiral allenes contain unique structural features poised to enable the tunable introduction of three new heteroatoms at each site of unsaturation (Scheme 1)
Transition metal-catalyzed allene amination methods complement those of conventional alkene oxidation for the synthesis of complex amine-containing stereotriads
A chemo, regio, and stereo-selective allene aziridination reaction furnishes key bicyclic methyleneaziridines (MA) that can be manipulated in diverse ways
Summary
2.1 Exocyclic bicyclic methyleneaziridines (MA) from sulfamate nitrene precursors The first challenge in developing oxidative allene amination methodologies was to identify robust methods to achieve chemo-, regio- and stereoselective allene aziridination. We found that AgOTf supported by bipyridine (bipy), 1,10-phenanthroline (phen), or dimethylbisoxazoline (tmbox) ligands resulted in excellent catalyst control over the chemoselectivity of the nitrene transfer event.[60,61,62] Approximately equimolar amounts of AgOTf and a phen ligand transformed allenes 6a-c of diverse substitution patterns selectively into MAs 7a-c with moderate-to-good E:Z ratios; the two isomers were separated by column chromatography.
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