In Situ-Generated Glycinyl Chloroaminals for a One-Pot Synthesis of Non-proteinogenic α-Amino Esters

Bench-stable imine surrogates for the one-pot and catalytic asymmetric synthesis of α-amino esters/ketones

N,O-Bis(tert-butoxycarbonyl)hydroxylamines are readily accessible as imine surrogates, which are bench stable and could quantitatively generate the corresponding imines for in situ applications. An unpresented catalytic asymmetric method for the synthesis of α-amino esters and ketones from novel imine surrogates, N,O-bis(tert-butoxycarbonyl)hydroxylamines, as well as its preliminary mechanistic studies are reported. A variety of optically enriched products were obtained in excellent yields and enantioselectivities (up to 99% yield and >99% ee).

A Broad Substrate Scope of Aza-Friedel-Crafts Alkylation for the Synthesis of Quaternary α-Amino Esters

A versatile synthetic protocol of aza-Friedel-Crafts alkylation has been developed for the synthesis of quaternary α-amino esters. This operationally simple alkylation proceeds under ambient conditions with high efficiency, regioselectivity, and an exceptionally broad scope of arene nucleophiles. A key feature of this alkylation is the role associated with the silver(I) salt counteranions liberated during the reaction. Taking advantage of a phase-transfer counteranion/Brønsted acid pair mechanism, we also report a catalytic enantioselective example of the reaction.

Catalyst-Free Synthesis of Polysubstituted 5-Acylamino-1,3-Thiazoles via Hantzsch Cyclization of α-Chloroglycinates

A catalyst-free heterocyclization reaction of α-chloroglycinates with thiobenzamides or thioureas leading to 2,4-disubstituted-5-acylamino-1,3-thiazoles has been developed. The methodology provides straightforward access to valuable building blocks for pharmaceutically relevant compounds.

Synthesis and Reactivity of α-Haloglycine Esters: Hyperconjugation in Action

A general and efficient synthesis of α-haloglycine esters from commercially available feedstock chemicals, in a single step, is reported. The reactivity of these α-haloglycine esters with various nucleophiles was studied as surrogates of α-iminoesters upon activation with hydrogen-bond donor catalysts. DFT calculations on the α-haloglycine structures (X = F, Cl, Br) accompanied by an X-ray characterization of the α-bromoglycine ester support the existence of a "generalized" anomeric effect created by hyperconjugation. This peculiar hyperconjugative effect is proposed to be responsible for the enhanced halogen nucleofugality leading to a facile halogen abstraction by hydrogen-bond donor catalysts. This reactivity was exploited with thiourea catalysts on several catalytic transformations (aza-Friedel-Crafts and Mannich reactions) for the synthesis of several types of non-proteinogenic α-amino esters.

Enantioselective Synthesis of α-Allyl Amino Esters via Hydrogen-Bond-Donor Catalysis

We report a chiral-squaramide-catalyzed enantio- and diastereoselective synthesis of α-allyl amino esters. The optimized protocol provides access to N-carbamoyl-protected amino esters via nucleophilic allylation of readily accessible α-chloro glycinates. A variety of useful α-allyl amino esters were prepared, including crotylated products bearing vicinal stereocenters that are inaccessible through enolate alkylation, with high enantioselectivity (up to 97% ee) and diastereoselectivity (>10:1). The reactions display first-order kinetic dependence on both the α-chloro glycinate and the nucleophile, consistent with rate-limiting C-C bond formation. Computational analysis of the uncatalyzed reaction predicts an energetically inaccessible iminium intermediate, and a lower energy concerted SN2 mechanism.

Total synthesis of (±)-fumimycin and analogues for biological evaluation as peptide deformylase inhibitors

A concise 7-step total synthesis of (±)-fumimycin in 11.6 % overall yield is reported. An acid-catalyzed intramolecular aza-Friedel-Crafts cyclization was developed to construct the benzofuranone skeleton of the natural product bearing an α,α-disubstituted amino acid moiety in a single step. Regioselective chlorination followed by a Suzuki-Miyaura cross-coupling rapidly enabled the preparation of a library of analogues which were evaluated against peptide deformylase for antibacterial activity.

Recent synthetic applications of α-amido sulfones as precursors of N-acylimino derivatives

α-Amido sulfones can be directly used as N-acylimine or N-acyliminium ion precursors in several synthetic processes aimed at the preparation of nitrogen containing compounds. This review collects the most relevant and practical utilizations of α-amido sulfones appeared in the literature after 2005.