Efficient synthesis of orthogonally protected anti-2,3-diamino acids

An asymmetric synthesis of anti-2,3-diamino acids is reported. The enolates of N,N-dibenzylated β³-amino esters were treated with di-tert-butyl azodicarboxylate (DBAD) to afford their N′,N″-di-Boc-2-hydrazino derivatives with excellent anti diastereoisomeric ratio. Final Boc removal and reductive cleavage of the hydrazino bond led to the expected 2,3-diamino esters having only one free amino group. In comparison with other asymmetric C-2 amination procedures, this method does not need the use of expensive chiral reagents and/or chiral auxiliaries, while leads to products which can be orthogonally protected.     

A facile synthetic method for chiral 1,2-epoxides and the total synthesis of chiral pheromone epoxides

Chiral 1,2-epoxy-3-alkanol tosylates were successfully synthesized from alkynols in three steps using the Sharpless AD reaction as a key step in good yields. Two chiral insect pheromone epoxides were smoothly obtained from the corresponding key intermediate.     

Nucleophilic addition to nitroacrylates: application towards the synthesis of 2,3-dehydroamino acids and 2,3-diamino acids

The addition of the N-pronucleophiles to 2- or 3-nitro-2-alkenoates in the presence of base provided Michael addition products. In the case of 3-nitro compounds, reaction occurred via the formation of α-adducts and the subsequent elimination of nitrous acid to produce olefins with high Z stereoselectivity. 3-Phthalimido-2-nitrocinnamate adduct 8a was converted into 2,3-diamino ester 11a.     

手性位移试剂Eu(dcm)~3的一个改进合成方法

我们对H(dcm)的Whitesides合成路线的关键步骤龙脑酰甲烷的合成和缩合反应进行了重要的改进。     

Enantioselective synthesis of chiral 1,2-diamines by the catalytic ring opening of azabenzonorbornadienes: application in the preparation of new chiral ligands

In the presence of a rhodium catalyst (5 mol %) generated in situ from [Rh(cod)Cl]₂ and (S,S′)-(R,R′)-C₂-ferriphos-tolyl, the asymmetric ring-opening reaction of N-Boc-azabenzonorbornadienes with dibenzylamine proceeded with excellent enantioselectivity (up to >99% ee) to give the corresponding 1,2-diamine scaffolds in high yields. The sequential deprotection of the ring-opened products and treatment with tartaric acid gave the enantiomerically pure 1,2-diamine tartrate salts. These salts were used for the preparation of new chiral ligands such as the salen-type ligands and Trost-type ligands.     

Catalytic dissymmetrization of meso-2-imidazolidinones: alternative route to chiral synthons for 1,2-diamines

The chiral functionalization of a simple heterocycle, 1,3-dihydro-2-imidazolone, was achieved by the highly enantioselective monodeacylation of meso-1,3-diacetyl-2-imidazolidinones via an oxazaborolidine-catalyzed borane reduction. This kinetically controlled dissymmetrization is sufficiently effective to provide a synthetic route to either enantiomer of (4S, 5S)- or (4R, 5R)-4,5-dimethoxy-2-imidazolidinone derivatives, which serve as chiral synthons for threo-1,2-diamines.     

A new insight into the Pfitzinger reaction. A facile synthesis of 6-sulfamoylquinoline-4-carboxylic acids

The unusual formation of 6-sulfamoylquinoline-4-carboxylic acids from 5-sulfamoylisatins under the conditions of Pfitzinger reaction is described. Key step in the suggested mechanism is the reaction of in situ generated acetaldehyde with the hydrolytically cleaved isatin ring. The suggested mechanism has been confirmed by dynamic LCMS measurements and by reactions with isotopically labeled reactants.     

A facile and convenient synthesis of functionalized ortho-nitrophenylboronic acids

A variety of ortho-nitrophenylboronic acids bearing functional groups such as cyano, nitro, halo, α-bromomethyl, and ester were prepared in good yields via I-Mg exchange followed by quenching with trimethyl borate. All reagents employed in this procedure are commercially available and were used without further purification, and the procedure can be executed in about an hour.     

A facile synthesis of 2,3-dihydroimidazo- and 1,2,3,4-tetrahydropyrirnido[1,2-f] phenanthridines

When 6-(2-hydroxyethyl)amino -(1 ), 6-(3-hydroxypropyl)amino -(2 ),or 6-[2-(1-hydroxybutyl)]-aminophenanthridines ( 3 ), dissolved in concentrated sulfuric acid, were treated with nitrosylsulfuric acid at 0–25, then diluted with water and basified with aqueous sodium hydroxide at 65–86°, 2,3-dihydroimidazo- ( 4a-i ), 1,2,3,4-tetrahydropyrimido- ( 5 ), or 2,3-dihydro-2-ethyl-imidazo[1,2-f]phenanthridines ( 4j-p ) were obtained respectively in good yields. Structures were substantiated by ir spectroscopy. The 6-ω-hydroxyalkylaminophenanthridines were prepared from the corresponding 6-chlorophenanthridines. A possible mechanism for the formation of these ring systems is postulated.     

Synthesis of new chiral cyclic 1,2-diamines and their evaluation as catalysts for enantioselective Diels-Alder reactions

The synthesis of new, enantiomerically pure cyclic 1,2-diamine structures was realized through a zinc promoted coupling of chiral bis-imines easily prepared starting from a chiral biphenyl dicarboxylic acid. The catalytic properties of such novel compounds were preliminarily studied; the trifluoroacetate salts of these chiral 1,2-diamines were shown to be able to catalyze the Diels-Alder reaction between cyclopentadiene and α,β-unsaturated aldehydes with good exo stereoselectivity and enantioselectivities up to 71%.     

A facile cleavage of oxirane with hydrazoic acid in dmf A new route to chiral β-hydroxy-α-amino acids

Chiral β-hydroxy-α-amino acids such as erythro-β-hydroxy-L-aspartic acid and erythro-β-hydroxymethyl-L-serine derivatives have been synthesized in optically pure form from L- and D-tartaric acids through a novel oxirane ring-opening reaction and a selective reduction of α-hydroxy ester as key steps.     

A new method for the synthesis of chiral beta-branched alpha-amino acids

A new method for the synthesis of chiral beta-branched alpha-amino acids based on a copper-mediated directed allylic substitution reaction with Grignard reagents is reported. This is the first case in which a delta-stereogenic center is controlling the diastereoselectivity of an o-DPPB-directed allylic substitution. Depending on the alkene geometry of the starting material either diastereomer, anti or syn, is accessible with good levels of acyclic stereocontrol.     

A 2,3-butanedione protected chiral glycine equivalent--a new building block for the stereoselective synthesis of enantiopure N-protected alpha-amino acids

A new chiral glycine equivalent 7 has been synthesised from glycidol using a chiral memory protocol, and its use in the synthesis of N-Z protected alpha-amino acids was demonstrated in a series of diasteroselective lithium enolate alkylation reactions and subsequent acid hydrolyses.     

Ferrier rearrangement for the synthesis of PEG-bound 2,3-unsaturated glycopyranosyl-amino acids

Amino acid 2,3-unsaturated glycopyranosyls have been prepared by the Ferrier rearrangement of acetyl protected glucals and PEG-bound amino acids in the presence of a catalytic quantity of BF₃·Et₂O in CH₂Cl₂ at ambient temperature.     

A new chiral diol derived from tetralone for the complexation of Lewis acids

A new approach to the rational design of Lewis acids based on face-face π-π interactions is described. The synthesis of two novel diols (−)(1R,3R)-2,2-dimethyl-1,2,3,4-tetrahydronaphthalene-1,3-diol (−)-1 and (−)(1S,3R)-trans-2,2-dimethyl-1,2,3,4-tetrahydronaphthalene-1-3-diol (−)-9 is reported in six and five steps respectively starting from α-tetralone. Complexation of (−)(1R,3R)-2,2-dimethyl-1,2,3,4-tetrahydronaphthalene-1,3-diol (−)-1 to phenylboronic acid shows the interplanar distance between the boron atom and the aromatic ring to be 3.05 Å, which is ideal for the proposed interactions.     

A facile route for the synthesis of vinyl-substituted 1,3,4-oxadiazoles

An efficient synthesis of vinyl-substituted 1,3,4-oxadiazoles using o-nitrophenyl sulfoxide precursor via syn-elimination reaction using sodium acetate in THF is described. This method is cost effective as it uses cheap o-nitrothiophenol and can be used in the synthesis of vinyl intermediates during synthesis of bioactive compounds, which avoids the use of any toxic metals.     

A new chiral catalyst for the enantioselective Strecker synthesis of alpha-amino acids

[reaction: see text] The chiral ammonium salt 3 is demonstrated to be an effective catalyst for the highly enantioselective Strecker reaction of N-allylbenzaldimines with hydrogen cyanide in CH2Cl2 solution.