Stefania Fioravanti

Facile and Highly Stereoselective One-Pot Synthesis of Either (E)- or (Z)-Nitro Alkenes

Aliphatic aldehydes were reacted with nitro alkanes in the presence of catalytic amounts of piperidine over 4 A molecular sieves. Simply by changing reaction conditions (solvent and temperature) it is possible to control the stereochemical outcome of the reactions, obtaining pure (E)- and (Z)-nitro alkenes in high to excellent yields. The role of molecular sieves on the stereochemical control seems crucial in addition to that of piperidine, especially for the synthesis of the Z isomer.

Solvent-free aziridination of α-nitroalkenes

Abstract NsONHCO 2 Et in the presence of CaO reacts without solvent with α-nitroalkenes to give 1-(ethoxycarbonyl)-2-nitroaziridines (62–84%). A possible involvement of an aza-Michael route is proposed on the basis of regio- and stereochemical reaction outcome, compared also with the results of thermolysis of ethyl azidoformate on the same α-nitroalkenes.

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.

Aziridination of α,β-unsaturated ketones

Abstract α,β-Unsaturated ketones are aziridinated by [(arenesulphonyl)oxy]carbamates and CaO (or Cs2CO3) or by N3CO2Et photolysis. A remote chiral center induced up to 74% d.e. Bis-unsaturated substrates showed scarce regioselectivity under all conditions.

Reagent-controlled diastereoselective aminations with a new chiral nosyloxycarbamate

The synthesis of a new chiral nosyloxycarbamate derived from Helmchens auxiliary is described. Reactions performed with this aminating reagent successfully give the formation of diastereomeric allylic carbamates or diastereomeric aziridines starting from different kinds of olefins.

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.

Easy access to α-amino β-oxo esters from β-enamino esters

Abstract N -Substituted α-amino β-oxo esters have been obtained by amination of β-enamino esters with ethyl N -[(4-nitrobenzenesulphonyl)oxy]carbamate (NsONHCO 2 Et), in the absence of added bases. The use of optically active pyrrolidines with C 2 symmetry as chiral auxiliaries induces diastereoselectivities up to 80%.

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.

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.

A novel route to N-substituted allylamines by the reaction of allylsilanes with (ethoxycarbonyl)nitrene☆

The reaction of mono- and disubstituted allylsilanes with (ethoxycarbonyl)nitrene allowed the preparation of the N-substituted allylamines 2a, 2b, 2e and 2d in yields up to 60%. The 2-ethoxyoxazolines 3a, 3b and 3c were isolated as minor products.