N,N-Diacylaminals as Emerging Tools in Synthesis: From Peptidomimetics to Asymmetric Catalysis

Second Generation Catalytic Enantioselective Nucleophilic Desymmetrization at Phosphorus (V): Improved Generality, Efficiency and Modularity

A broadly improved second generation catalytic two-phase strategy for the enantioselective synthesis of stereogenic at phosphorus (V) compounds is described. This protocol, consisting of a bifunctional iminophosphorane (BIMP) catalyzed nucleophilic desymmetrization of prochiral, bench stable P(V) precursors and subsequent enantiospecific substitution allows for divergent access to a wide range of C-, N-, O- and S- substituted P(V) containing compounds from a handful of enantioenriched intermediates. A new ureidopeptide BIMP catalyst/thiaziolidinone leaving group combination allowed for a far wider substrate scope and increased reaction efficiency and practicality over previously established protocols. The resulting enantioenriched intermediates could then be transformed into an even greater range of distinct classes of P(V) compounds by displacement of the remaining leaving group as well as allowing for even further diversification downstream. Density functional theory (DFT) calculations were performed to pinpoint the origin of enantioselectivity for the BIMP-catalyzed desymmetrization, to rationalize how a superior catalyst/leaving group combination leads to increased generality in our second-generation catalytic system, as well as shed light onto observed stereochemical retention and inversion pathways when performing late-stage enantiospecific SN2@P reactions with Grignard reagents.

Organocatalytic Michael Addition of Unactivated α-Branched Nitroalkanes to Afford Optically Active Tertiary Nitrocompounds

The direct, asymmetric conjugate addition of unactivated α-branched nitroalkanes is developed based on the combined use of chiral amine/ureidoaminal bifunctional catalysts and a tunable acrylate template to provide tertiary nitrocompounds in 55-80% isolated yields and high enantioselectivity (e.r. up to 96:4). Elaboration of the ketol moiety in thus obtained adducts allows a fast entry to not only carboxylic and aldehyde derivatives but also nitrile compounds and enantioenriched 5,5-disubstituted γ-lactams.

Brønsted Base-Catalyzed Enantioselective α-Functionalization of Carbonyl Compounds Involving π-Extended Enolates

Chiral Brønsted base (BB) catalyzed asymmetric transformations constitute an important tool for synthesis. A meaningful fraction of these transformations proceeds through transiently generated enolate intermediates, which display quite versatile reactivity against a variety of electrophiles. Some years ago, our group became interested in developing BB-catalyzed asymmetric reactions of enolizable carbonyl substrates that involve π-extended enolates in which, besides control of reaction diastereo and enantioselectivity, the site-selectivity control is an additional issue in most cases. In the examples covered in this account the opportunities deployed, and the challenges posed, by these methods are illustrated, with a focus on the generation of quaternary carbon stereocenters. In the way, new bifunctional BB catalysts as well as achiral templates were developed that may find further applications.

Accessing Chiral Pyrrolodiketopiperazines under Organocatalytic Conditions

The production of chiral pyrrolodiketopiperazines under organocatalytic conditions demonstrates the capacity of bicyclic acylpyrrol lactims to perform as pronucleophiles in direct carbon-carbon bond forming reactions. The good performance of ureidoaminal-derived Brønsted bases in the Michael addition to nitroolefins affords these heterocyclic scaffolds with high skeleton diversity.

Photoinduced α-C-H Amination of Cyclic Amine Scaffolds Enabled by Polar-Radical Relay

Herein, we report a polar-radical relay strategy for α-C-H amination of cyclic amines with N-chloro-N-sodio-carbamates. The relay is initiated by in situ generation of cyclic iminium intermediate using N-iodosuccinimide (NIS) oxidant as an initiator, which then operates through a series of polar (addition and elimination) and radical (homolysis, hydrogen- and halogen atom transfer) reactions to enable the challenging C-N bond formation in a controlled manner. A broad range of α-amino cyclic amines were readily accessed with excellent regioselectivity, and the superb applicability was further demonstrated by functionalization of biologically relevant compounds.

Synthesis of β-Hydroxy α-Amino Acids Through Brønsted Base-Catalyzed syn-Selective Direct Aldol Reaction of Schiff Bases of Glycine o-Nitroanilide

Here we report the highly enantio- and syn-selective synthesis of β-hydroxy α-amino acids from glycine imine derivatives under Brønsted base (BB) catalysis. The key of this approach is the use of benzophenone-derived imine of glycine o-nitroanilide as a pronucleophile, where the o-nitroanilide framework provides an efficient hydrogen-bonding platform that accounts for nucleophile reactivity and diastereoselectivity.

A Carbodiimide-Mediated P-C Bond-Forming Reaction: Mild Amidoalkylation of P-Nucleophiles by Boc-Aminals

The first example of a carbodiimide-mediated P-C bond-forming reaction is described. The reaction involves activation of β-carboxyethylphosphinic acids and subsequent reaction with Boc-aminals using acid-catalysis. Mechanistic experiments using ³¹P NMR spectroscopy and DFT calculations support the contribution of unusually reactive cyclic phosphinic/carboxylic mixed anhydrides in a reaction pathway involving ion-pair "swapping". The utility of this protocol is highlighted by the direct synthesis of Boc-protected phosphinic dipeptides, as precursors to potent Zn-aminopeptidase inhibitors.