M. Antonietta Loreto

Noncovalent Organocatalysis: A Powerful Tool for the Nucleophilic Epoxidation of α-Ylideneoxindoles

A novel asymmetric nucleophilic epoxidation for α-ylideneoxindole esters has been successfully devised, resulting in enantioenriched spiro compounds with two new contiguous stereocenters. The employed (S)-α,α-diphenylprolinol functions as a bifunctional catalyst, creating a complex H-bond network in conjunction with a substrate and an oxidant.

Aziridination of α,β-unsaturated esters by (ethoxycarbonyl)nitrene

Abstract The reaction of α,β-unsaturated esters with (ethoxycarbonyl)nitrene, generated by α-elimination of NsONHCO 2 Et using CaO as a base in heterogeneous phase, allowed the preparation of aziridine-1,2-dicarboxylates ( 2a-e ) in good isolated yields (57–72%). The same reaction does not take place using triethylamine instead of CaO, in homogeneous conditions.

Asymmetric synthesis of N-substituted α-amino esters

Abstract A one pot procedure converting chiral silyl ketene acetals to N -substituted α-amino esters by amination with ethyl azidoformate is described.

Asymmetric formation of CN bonds in chiral enol ethers

Abstract Attack of EtO 2 CN on an enol ether carrying ( S , S )-hydrobenzoin as chiral auxiliary gives diastereoselective aziridination with diastereomeric excess > 95%. Easy subsequent hydrolysis gives partially racemised α-amino ketone 4 . Other chiral auxiliaries does not allow isolation of intermediate aziridines and the α-amino ketone is isolated with a 75:25 enantiomeric ratio. The thermolysis of EtO 2 CN 3 in most of the same enol ethers gives the acetals of the α-amino ketone with prevailing opposite configuration at the new formed chiral centre.

Asymmetric addition of ethyl azidoformate to optically active enamines. Reversal of facial selectivity compared with (ethoxycarbonyl)nitrene

Abstract Thermal reaction of ethyl azidoformate with proline-derived optically active enamines of cyclohexanone, followed by photolysis, proceeds with opposite facial selectivity to that observed using (ethoxycarbonyl)nitrene. A tentative explanation is proposed. The absolute configuration of the main product, 2-(ethoxycarbonylamino)cyclohexanone ( 6 ), was deduced by chemical correlation.

Pyridinium Chloride in Three Membered Ring Opening. Synthesis of Chlorohydrins

Abstract Despite the fact that pyridinium chloride has been reported1 as a reagent in the quantitative analysis of oxiranes, we know only two examples of the use of pyridinium iodide, in pyridine, for preparative purpose. The products isolated in that solvent were the corresponding quaternary salts2 derived from the iodohydrins, along with a large amount of ketone .(up to 90% in the case of 1,2-epoxycyclohexane). Even the use of a “sophisticated reagent” such as dichlorobis(benzonitrile) palladium(II) results in the formation of a good quantity (30% in the case of 1,2-epoxycyclohexane) of α-chloro ketone as byproduct.3 Unsymmetrically substituted oxiranes open under acidic conditions to give variable amounts of the two possible products according to reaction conditions. The best regioselectivity was observed, for example, using hydrogen chloride in diethyl ether

Synthesis of α-amino γ-butyrolactone derivatives by aziridination of α-ylidene γ-butyrolactones

The reactions of exocyclic α,β-unsaturated γ-lactones with NsONHCO2Et and CaO produce N-(ethoxycarbonyl) spiroaziridino γ-lactones. By reaction with acetic acid these products give ring opening reaction and acetylated N-protected α-amino γ-butyrolactones are obtained. The ring opening reaction is quantitative and highly regioselective.

Aziridination of α,β-unsaturated phosphonic esters

Abstract Synthetic precursors of amino phosphonic acids are aziridinyl phosphonates. These compounds can be prepared through a reaction of phosphonates 2a–e with NsONHCO2Et and inorganic bases involving addition of an (ethoxycarbonyl)amino group onto the double bond, via a new and easy procedure.

Improved amination by ethyl n-(4-nitrophenyl)sulphonyloxy carbamate in the presence of inorganic oxides or carbonates

Abstract Inorganic solid bases give rise to α-elimination reactions of NsONHCO2Et under easy and mild conditions without catalyst or ultrasounds. For several kinds of substrates, a comparison of yields and reaction times with previous methods is presented.

α-Methylene β-amino phosphonic ester derivatives by amination of (1-trimethylsilanylmethyl-vinyl) phosphonic esters

Abstract (1-Trimethylsilanylmethyl-vinyl)-phosphonic esters are synthesised via Wittig–Horner reactions starting from methylenediphosphonic esters. The reactions of (1-trimethylsilanylmethyl-vinyl)-phosphonic esters with NsONHCO2Et and CaO, produce α-methylene N-(ethoxycarbonyl) β-amino phosphonic esters, isolated up to 60% yield, through addition of (ethoxycarbonyl) amine function on the double bond and silyl group elimination.