Enantioenriched α-substituted glutamates/pyroglutamates via enantioselective cyclopropenimine-catalyzed Michael addition of amino ester imines

• Zara M. Seibel,
• Jeffrey S. Bandar and
• Tristan H. Lambert

Beilstein J. Org. Chem. 2021, 17, 2077–2084, doi:10.3762/bjoc.17.134

• -substituted glutamate derivatives is via the Michael addition of α-amino ester enolates to acrylate acceptors. These products can also be easily converted to pyroglutamates by lactamization [28][29][30]. Although the use of substituted amino ester derivatives for the enantioselective α-alkylation has been

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• high diastereoisomeric purities [74] (Scheme 37). The deoxyfluorination of the enantiopure α-hydroxy-β-amino ester 152a or α-amino-β-hydroxyphenylalanine ester 155 [74][75][76] under the same conditions proceeded via aziridinium ion 156 and generated β-fluoro-α-amino ester 153a in good yield and high

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• in the presence of 2,6-lutidine to generate α-amino ester 71 (99%, Scheme 24) [61]. Alkylidenecyclopropanes resulting from the Ireland–Claisen rearrangement of cyclopropenylcarbinyl glycolates and glycinates can serve as useful precursors of other classes of functionalized cyclopropanes. As shown

• reactions which were applied to α-hydroxy esters 74 and 75 using N-iodosuccinimide (MeCN/H2O, 50 °C) [70], or to the N-benzylamine generated from α-amino ester 71 (by reductive animation with benzaldehyde) in the presence of I2 and K2CO3 (MeCN, rt) [71]. These iodocyclizations led to the oxabicyclic

Unnatural α-amino ethyl esters from diethyl malonate or ethyl β-bromo-α-hydroxyiminocarboxylate

• Eloi P. Coutant,
• Vincent Hervin,
• Glwadys Gagnot,
• Candice Ford,
• Racha Baatallah and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2853–2860, doi:10.3762/bjoc.14.264

• -bromo-α-hydroxyiminocarboxylate and various alkylfuranes. Keywords: α-amino ester; α-hydroxyimino ester; [2 + 4] cycloadditions; [2 + 3] cycloadditions; Knoevenagel; nitrosoacrylate; Suzuki–Miyaura; Introduction Our current work on the chemistry of imidazo[1,2-a]pyrazin-3(7H)-one luciferins [1] has

• (hydrochloric and powdered zinc) and we successfully used instead the much milder [34] mixture of ammonium formate and zinc in ethanol at room temperature to give 43% of the target α-amino ester 53. The same strategy gave the corresponding α-amino ester homolog 58 from the readily available dioxane derivative

• alternative for the preparation of many furan-bearing α-amino esters. Malonate-based retrosynthesis of α-amino esters. Some side products and synthesis of α-amino ester 10. Syntheses of α-amino esters 22, 24, 26, 28 and 33. Syntheses of α-amino esters 38, 41 and 46a,b. Syntheses of α-amino esters 53 and 58

Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions

• Glwadys Gagnot,
• Vincent Hervin,
• Eloi P. Coutant,
• Sarah Desmons,
• Racha Baatallah,
• Victor Monnot and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2846–2852, doi:10.3762/bjoc.14.263

• -amino esters was achieved using gold(I) chemistry. Keywords: α-amino ester; α-nitro esters; cerium ammonium nitrate; cycloaddition; gold(I) cyclization; Introduction In the course of our work on an original synthesis of imidazo[1,2-a]pyrazin-3(7H)-one luciferins [1], a large variety of racemic α-amino

• acid in ethanol overnight gave a sufficient amount of the (pure) target phenyl-bearing α-amino ester 10 which had been previously obtained by catalytic hydrogenation using palladium [20]. The same transformation sequences were used starting with compound 6n and provided the furan-bearing α-amino ester

• reduction of 13 using zinc and hydrochloric acid gave the target α-amino ester 14 in an 85% yield. To avoid the recourse to more rare and/or expensive heterocyclic aldehydes, we also tried synthetic approaches based on [2 + 3] cycloadditions. As depicted in Scheme 3, the carbon dioxide-producing reaction

Synthesis of a leopolic acid-inspired tetramic acid with antimicrobial activity against multidrug-resistant bacteria

• Luce Mattio,
• Loana Musso,
• Leonardo Scaglioni,
• Andrea Pinto,
• Piera Anna Martino and
• Sabrina Dallavalle

Beilstein J. Org. Chem. 2018, 14, 2482–2487, doi:10.3762/bjoc.14.224

• could be a Lacey–Dieckmann cyclization starting from a N-acetoacetyl-α-amino ester. Interestingly, the biosynthetic pathways of the tetramic acid scaffold involves Lacey–Dieckmann cyclases [23] or a spontaneous intramolecular Claisen condensation, which occurs in the cytosol. To protect the α-amino

• ester nitrogen we chose the p-methoxybenzyl (PMB) group, easily removable by ceric ammonium nitrate (CAN). N-(4-Methoxybenzyl)glycine ethyl ester (5) was obtained in 87% yield by reacting 4-methoxybenzylamine (3) with bromoacetic acid ethyl ester (4) in THF (Scheme 1). The ester 5 was converted into

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• nucleophiles for the conjugate addition–enantioselective protonation of α-aminoacrylates (vide infra). In 2010, Mikami and co-workers reported a hydrogen atom transfer strategy for the synthesis of β-perfluorobutyl-α-amino ester 13 in low yield and modest enantioselectivity, and the absolute configuration of

Synthesis of chiral N-phosphinyl α-imino esters and their application in asymmetric synthesis of α-amino esters by reduction

• Yiwen Xiong,
• Haibo Mei,
• Lingmin Wu,
• Jianlin Han,
• Yi Pan and
• Guigen Li

Beilstein J. Org. Chem. 2014, 10, 653–659, doi:10.3762/bjoc.10.57

• chromatography and recrystallization. The chiral phosphinyl auxiliary could be easily cleaved under acidic conditions. Keywords: α-amino ester; α-imino ester; group-assisted purification; phosphinyl auxiliary; reduction; Introduction α-Imino esters play a very important role in the field of imine chemistry [1

• protected α-amino ester 4. Typical sulfinyl (a), phosphonyl aldimines (b) and phosphinyl imino esters (c). Synthesis of α-imino ester by rearrangement. Cleavage of the chiral auxiliary. Optimization of the synthesis of α-imino ester 3a by the condensation method.a Synthesis of N-phosphinyl-protected α-imino

Arylglycine-derivative synthesis via oxidative sp³ C–H functionalization of α-amino esters

• Zhanwei Xu,
• Xiaoqiang Yu,
• Xiujuan Feng and
• Ming Bao

Beilstein J. Org. Chem. 2012, 8, 1564–1568, doi:10.3762/bjoc.8.178

• phenols with α-amino esters proceeded smoothly in the presence of meta-chloroperoxybenzoic acid as an oxidant under ambient conditions, to produce arylglycine derivatives in satisfactory yields. Keywords: α-amino ester; arylglycine; C–H functionalization; oxidation; synthesis; Findings Arylglycine