Synthesis of β,β-branched β-amino ester derivatives through spiroaziridination of (α-trimethylsilanylmethyl)cyclohexylidene esters

The reaction of (α-trimethylsilanylmethyl)cyclohexylidene esters with NsONHCO₂Et and CaO produces the N-(ethoxycarbonyl)spiroaziridines which, after ring-opening, gives the corresponding β,β-disubstituted β-amino ester derivatives. The stereochemical outcome of the reaction is influenced by substituents on the cyclohexyl group.     

Regio- and diastereoselective Reformatsky reaction of chiral fluoroalkyl α,β-unsaturated N-tert-butanesulfinyl ketimines: Efficient asymmetric synthesis of β-fluoroalkyl β-vinyl β-amino esters

Highly regio- and diastereoselective Reformatsky reaction of stable, chiral fluoroalkyl α,β-unsaturated N-tert-butanesulfinyl ketimines was developed, which provided an efficient method for the asymmetric synthesis of structurally diverse β-tetrasubstituted β-fluoroalkyl β-vinyl β-amino esters in good yields and with excellent diastereoselectivities (dr up to 96:4).     

Synthesis of β-amino carbonyl compounds via a Zn(OTf)2-catalyzed cascade reaction of anilines with aromatic aldehydes and carbonyl compounds

A Zn(OTf)₂-catalyzed cascade reaction of anilines with aromatic aldehydes and carbonyl compounds was described. This one-pot three-component reaction afforded the corresponding β-amino carbonyl compounds, β-amino esters, and β-amino ketones in good to excellent yields. The reaction was also applied for the liquid-phase synthesis of β-amino carbonyl compound library using PEG as a support.     

An efficient synthesis of (E)-α,β-unsaturated ketones and esters with total stereoselectivity by using chromium dichloride

(E)-α,β-Unsaturated ketones 1 or esters 2 can be obtained with complete stereoselectivity by reaction of different 2-chloro-3-hydroxy ketones 3 or esters 4 and CrCl₂. A comparative study of the results of synthesis of ketones 1 with CrCl₂ or samarium is performed. A mechanism to explain both β-elimination reactions has been proposed.     

Ir-catalyzed chemoselective reduction of β-amido esters: A versatile approach to β-enamino esters

The conversion of β-amido esters to β-enamino esters is an indispensable step for some synthetic approaches to alkaloids and related medicines. Known methods for such transformation are not only stepwise, but also proceed with low atom-efficiency. Herein, we report a direct and versatile approach that features the Ir-catalyzed chemoselective reduction of β-amido esters with 1,1,3,3-tetramethyldisiloxane (TMDS). In addition, a lack of some signals was observed in the ¹³C NMR spectra of some alicyclic β-enamino esters. This revealed a longstanding existing but being ignored phenomenon in the literature.     

Regio- and stereoselective double alkylation of β-enamino esters with organolithium reagents followed by one-pot reduction: convenient method for the synthesis of tertiary γ-amino alcohols

An easy, high yielding and stereoselective procedure for the preparation of tertiary γ-amino alcohols starting from β-enamino esters is presented. In this procedure, the double alkylation of β-enamino esters with organolithium reagents is followed by one-pot reduction with sodium borohydride in methanol/acetic acid. A hypothesis of mechanism is given, explaining the observed diastereoselectivity through molecular modeling. The configuration of the products was determined by ¹H NMR spectroscopy coupled with conformational analysis.     

New approach to exclusive formation of both enantiomers of β-amino acid derivatives

A highly selective two-step approach to chiral β-amino esters via the hydride reductive amination of chiral allenes is reported. β-Enamino esters were obtained from the nucleophilic addition of amines to 2,3-allenoates bearing a chiral auxiliary. The reduction of the (1R)-(−)-10-phenylsulfonylisobornyl β-enamino esters gave the corresponding β-amino esters with S configuration whereas the reduction of the (1S)-(+)-10-phenylsulfonylisobornyl β-enamino esters led to β-amino esters with R configuration. The rationalization of the observed selectivity was supported by semi-empirical molecular orbital calculations (PM3).     

Nitroalkanes and ethyl glyoxalate as common precursors for the preparation of both β-keto esters and α,β-unsaturated esters

β-Nitro acrylic esters, obtained by the reaction of nitroalkanes and ethyl glyoxalate, are the key building blocks for the immediate synthesis of both the title compounds. In fact, their treatment with titanium trichloride produce the direct conversion to the β-keto esters, while their reaction with sodium boron hydride gives the one-pot synthesis of α,β-unsaturated esters through formal substitution of the vinylic nitro group with an hydrogen.     

N-Methyl indoxyl Esters as Substrates for Cholinesterase

Abstract

Several esters were prepared as substrates for cholinesterase: the acetate, propionate and butyrate esters of N-methyl indoxyl, umbelliferone acetate, and the acetate and butyrate esters of 4-methyl umbelliferone. Comparison of these substrates with other fluorogenic esters: indoxyl acetate, indoxyl butyrate, resorufin acetate, B-carbonaphthoxycholine, and β-naphthyl acetate indicated that N-methyl indoxyl butyrate was the best substrate for pseudo cholinesterase. Analysis of as little as 5 × 10^?6 units per ml. of cholinesterase can be performed by a direct initial reaction-rate method in 2–3 minutes with an accuracy and precision of about 1.5%.     

Synthesis of (Z)-α-chloro-α,β-unsaturated esters with complete stereoselectivity promoted by samarium diiodide

Stereoselective β-elimination in α,α-dichloro-β-hydroxyesters 2 was achieved by using samarium diiodide, yielding (Z)-α-chloro-α,β-unsaturated esters 1. The starting compounds 2 were easily prepared by reaction of the lithium enolate of ethyl dichloroacetate with different aldehydes at −78 °C. A mechanism to explain this process is proposed.     

A mild and environmentally acceptable synthetic protocol for chemoselective α-bromination of β-keto esters and 1,3-diketones

A wide variety of unsubstituted β-keto esters can be brominated chemoselectively to the corresponding α-monobromo-β-keto esters by using a combination of vanadium pentoxide, hydrogen peroxide and ammonium bromide in a biphasic system, dichloromethane-water at 0-5 °C. In addition, α-mono substituted β-keto esters, cyclic β-keto-esters and 1,3-diketones can also be brominated selectively using the same protocol.     

Organic-salt-mediated highly regioselective N3-alkylation of 2-thiophenytoin via Michael reaction under solvent-free conditions

A regioselective N3-alkylation of 5,5-diphenyl-2-thiohydantoin (2-thiophenytoin) using a very efficient mild base K₂CO₃ and α,β-unsaturated esters in the presence of organic salt TBAB (tetrabutylammonium bromide) at room temperature has been reported (3b–3h). The selectivity of this reaction is excellent and products have been produced in good yields under solvent-free conditions. The increase of the reaction temperature to 70°C mostly disappeared this selectivity and afforded only the N1,N3-dialkylated derivatives of 2-thiophenytoin in good yields (4b–4g). We were unable to selectively N3-alkylate 2-thiophenytoin with ethyl acrylate at both room temperature and 70°C under the same conditions (4a). Dimethyl and diethyl fumarates cannot work as Michael acceptors and were hydrolyzed to fumaric acid under reaction conditions.     

Transition-metal,organic solvent and base free α-hydroxylation of β-keto esters and β-keto amides with peroxides in water

Without employing any transition metal, organic solvent and base, a facile, economical and environmentally friendly strategy has been developed for the α-hydroxylation of β-keto esters and β-keto amides with peroxides via radical cross-coupling reaction in water under open-air conditions. This protocol allows a convenient access to various α-hydroxy-β-keto esters and α-hydroxy-β-keto amides with up to 92% yield (34 examples). Moreover, the reaction was successfully scaled up to gram quantity and mechanistic studies showed the radical pathway was involved in this hydroxylation.     

Studies on the Silylation Reaction of α,β-Epoxy Esters Synthesized by Darzen's Condensation Reaction

Me₃SiCl/Mg in HMPA was used for silylation of α,β-epoxy esters resulting in the corresponding β-silylated esters in a one pot reaction with reasonable yields.     

Ultrasound-assisted rapid synthesis of β-cyanoepoxides using hypervalent iodine reagents

An elegant approach for the rapid synthesis of β-cyanoepoxides 3 by the epoxidation of β-cyanostyrenes 1 with PIDA 2a is described. The epoxidation of β-cyanostyrenes 1 was performed with 1.2 equiv. of PIDA 2a in MeCN-H₂O (1:1) at room temperature in ultrasonic bath. The epoxidation reactions were completed in short reaction time and β-cyanoepoxides 3 were isolated in 69–94% yields.     

REACTION BETWEEN 2-HYDROXY ESTERS OF HYPOPHOSPHOROUS ACID AND ALCOHOLS

Abstract

A study of the reaction between esters of hypophosphorous acid and alcohols is carried out. It has been established that the 2-hydroxy esters of hypophosphorous acid react with alcohols as a result of which phosphonous acids are formed. A possible scheme of this reaction is suggested.     

Quinoxaline synthesis in novel tandem one-pot protocol

A variety of quinoxalines were synthesized via tandem one-pot procedure for the first time in water medium. The key strategy was the in situ preparation of α-halo-β-keto esters by the reaction of N-bromo succinimide with β-keto esters and further condensation with phenylene diamines. This novel eco-friendly approach offers an easy, efficient, and mild synthesis of highly substituted quinoxalines in good yields.     

NaNO2-Ceric ammonium nitrate mediated conversion of acrylic esters and Baylis-Hillman derived acrylic esters into corresponding β-nitro acrylic esters

A variety of acrylic esters, including those derived from Baylis-Hillman reactions, react with NaNO₂-ceric ammonium nitrate to form the corresponding β-nitro alcohols 2 and 5 whose dehydration, via their mesylates, leads to β-nitro acrylic esters, in good to excellent yields. Further, β-nitro acrylic esters containing a mesylate group 6, obtained from the Baylis-Hillman products, react with NaN₃ to form 2-cyano-3-substituted acrylic esters 10 in excellent yields.     

Preparation and Reactions of 2-Oxa-6-thiabicyclo[3.2.0]-heptanes and 2-Oxa-5-thiabicyclo[2.2.1]heptanes from Pentoses

Abstract:

The preparation of the two diastereoisomeric 3-methoxy-2-oxa-6-thiabicyclo-[3.2.0]heptan-4-ols 4 and 5 from D-xylose 1 via methyl 2,3-anhydro-α-D-ribofuranoside and the corresponding β-anomer is described. Oxidation of 4 and 5 yields the sulfoxides 6 and 7 and the sulfones 8. – On the other hand, the two diastereoisomeric 3-methoxybicyclo[2.2.1]heptan-7-ols 11 and 12 are obtained from methyl 5-acetylthio-5-deoxy-2-O-mesyl-D-xylofuranosides 9 and 10 via Mitsunobu reaction and intramolecular cyclization. – The stereoisomeric counterparts of 4 and 5, 13 and 14, are obtained in only four steps from L-arabinose.