Optically active aromatic and heteroaromatic alpha-amino acids by a one-pot catalytic enantioselective addition of aromatic and heteroaromatic C-H bonds to alpha-imino esters

Enantioselective synthesis of α-tetrasubstituted (1-indolizinyl) (diaryl)-methanamines via chiral phosphoric acid catalysis

An enantioselective Friedel-Crafts reaction of cyclic α-diaryl N-acyl imines with indolizines catalyzed by a chiral spirocyclic phosphoric acid has been developed. The asymmetric transformation proceeds smoothly to afford α-tetrasubstituted (1-indolizinyl) (diaryl)methanamines in good yields with up to 98% ee under mild conditions.

Sulfuric Acid Catalyzed Esterification of Amino Acids in Thin Film

The esterification reaction of different amino acids with methanol catalyzed by H2SO4 was first studied in the small volume of thin films generated by ESI microdroplet deposition. The reaction is promoted by the pneumatic spray of the ESI source and reaches its maximum efficiency at a thin film temperature of 70 °C. Selective esterification of the COOH moiety was demonstrated. Microdroplet size and thin film volume and lifetime are critical parameters that influenced the reaction outcome. As expected, l-tyrosine and l-phenylalanine having aromatic side chain substituents were the most reactive amino acids, reaching absolute yields of around 40-50%. The amino acid esterification catalyzed by H2SO4 in a thin film occurs under synthetic conditions in which the same reaction in the bulk is not observed.

Enantioselective Friedel-Crafts Reaction of Heteroaromatic Compounds with Glyoxals Catalyzed by Chiral Oxazaborolidinium Ion Catalyst

A catalytic enantioselective Friedel-Crafts reaction of various heteroaromatic compounds with glyoxals has been developed. In the presence of a chiral oxazaborolidinium ion catalyst, the reaction provided chiral α-hydroxyketones in high yield (up to 96%) with excellent enantioselectivity (up to >99% ee). The synthetic utility of this method was illustrated by conversion of the products to various derivatives such as 1,2-diol and β-amino alcohol.

Enantioselective synthesis of α-tetrasubstituted (3-indolizinyl) (diaryl)methanamines via chiral phosphoric acid catalysis

An enantioselective Friedel-Crafts reaction of cyclic α-diaryl N-acyl imines with indolizines catalyzed by a chiral spirocyclic phosphoric acid has been developed. The asymmetric transformation proceeds smoothly to afford α-tetrasubstituted (3-indolizinyl) (diaryl)methanamines in good yields with up to 98% ee under mild conditions.

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.

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

An acetyl chloride-mediated cascade transformation involving a primary carbamate, ethyl glyoxylate, and various types of nucleophiles is reported for the synthesis of orthogonally protected α-amino esters. These reactions proceeded rapidly to afford the pivotal α-chloroglycine intermediate in excellent yields, which can be directly functionalized in situ with various types of nucleophiles. A mild and unique AcOH(cat.)/AcCl system was found to promote an autocatalytic-like condensation and facilitate the multicomponent assembly of non-proteinogenic α-amino esters. To better understand this one-pot transformation and the orchestration of the components' condensations, the investigation of a broader scope of nucleophiles and some kinetic studies are presented. Our findings suggest that the halogenation step toward the formation of α-chloroglycine is the rate-determining step likely proceeding through the formation of N-carbamoyl iminium. Also, the initial kinetic profiling for the nucleophilic substitution supports an S_N1-like (S_N2C+) mechanism in which nucleophiles add to the iminium-chloride tight ionic pair. These results lead ultimately to the design of a new protocol in which an achiral hydrogen bond donor thiourea catalyst was utilized to enhance the reaction scope and enable silylated nucleophiles to be efficiently exploited to synthesize novel non-proteinogenic α-amino esters.

Chiral Brønsted Acid Catalyzed Enantioselective aza-Friedel-Crafts Reaction of Cyclic α-Diaryl N-Acyl Imines with Indoles

Asymmetric addition of indoles to cyclic α-diaryl-substituted N-acyl imines, which are generated in situ from 3-aryl 3-hydroxyisoindolinones, is described. The transformation proceeds smoothly with a broad range of indoles and isoindolinone alcohols using a SPINOL-derived chiral Brønsted acid catalyst to afford α-tetrasubstituted (3-indolyl)(diaryl)methanamines in excellent yields and enantioselectivities (up to 98% yield, up to >99:1 e.r.). The origin of stereochemical induction is supported by DFT calculations and experimental data.

Tandem processes identified from reaction screening: nucleophilic addition to aryl N-phosphinylimines employing La(III)-TFAA activation

Reaction screening of nucleophilic reaction partners for addition to N-diphenylphosphinylimines employing lanthanum(III) triflate as a catalyst and trifluoroacetic anhydride (TFAA) as an activator is reported. A number of tandem processes leading to novel chemotypes including aza-Prins/intramolecular Friedel-Crafts annulations have been identified, and both reaction scope and mechanism further investigated.

Asymmetric synthesis of aminochromanes via intramolecular indium-mediated allylation of chiral hydrazones

The asymmetric intramolecular indium-mediated cyclization reaction delivers chromanes with excellent diastereoselectivity (68-91% yield, dr >99:1). The reaction was efficient for aryl substrates with both electron-withdrawing and -donating groups. Carboxylic acid additives were found to be necessary for optimal reaction.

Catalytic C-H functionalization by metal carbenoid and nitrenoid insertion

Novel reactions that can selectively functionalize carbon-hydrogen bonds are of intense interest to the chemical community because they offer new strategic approaches for synthesis. A very promising 'carbon-hydrogen functionalization' method involves the insertion of metal carbenes and nitrenes into C-H bonds. This area has experienced considerable growth in the past decade, particularly in the area of enantioselective intermolecular reactions. Here we discuss several facets of these kinds of C-H functionalization reactions and provide a perspective on how this methodology has affected the synthesis of complex natural products and potential pharmaceutical agents.

SiO2-Supported CeCl3·7H2O−NaI Lewis Acid Promoter: Investigation into the Garcia Gonzalez Reaction in Solvent-Free Conditions⊥

The Knoevenagel condensation of aldose sugars with beta-dicarbonyl compounds produces furan derivatives having polyhydroxyalkylated alkyl side chains; this reaction is known as the Garcia Gonzalez reaction. Despite the fact that these polyhydroxyalkyl furans are interesting scaffolds for synthetic chemists to utilize in the synthesis of a variety of biologically interesting molecules, the reported approach suffers from harsh conditions. The development of a general and more efficient protocol is of considerable importance, and in this manuscript, we wish to explore the role of the NaI in enhancing the activity of CeCl3.7H2O as a useful water-tolerant Lewis acid promoter for the Garcia Gonzalez reaction. The procedure proceeds with good yields at 50 degrees C using our system supported on SiO2 in solvent-free conditions and represents a simple and convenient methodology for the preparation of densely functionalized molecules. Furthermore, the first qualitative results obtained on mechanistic investigation on the role of iodide on this our heterogeneous reaction may be of value for optimization of existing organic transformations and for the development of new ones.

Catalytic asymmetric addition of dialkylzinc reagents to alpha-aldiminoesters

[reaction: see text] The first catalytic, enantioselective addition of organozinc reagents to alpha-aldiminoesters is described. The use of a Lewis acid/Lewis base containing bifunctional catalyst preorganizes both reactive substrates to promote enantioselective addition over the racemic background reaction and alternative addition modes. Alcohol additives were found to enhance the enantioselection. The addition product was also found to cyclize with remaining substrate to provide imidazolidines.