Aliphatic aldehydes were reacted with nitro alkanes in the presence of catalytic amounts of piperidine over 4 Å 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.
(
E)-Trifluoromethyl imines were considered as ideal substrates to be transformed into the corresponding diaziridines by a direct amination reaction with nosyloxycarbamates. The diastereoselective ...induction was strongly controlled by the
N-substituent. Similar results were obtained in the epoxidation reactions performed on the same substrates using
m-CPBA as oxidant. Starting from enantiopure imines chiral diaziridines or oxaziridines were obtained with very high enantiopurity.
Display omitted
(
E)-
O-Arylsulfonyl-
N-(2-nitroalk-2-enyl)hydroxylamines were easily obtained in good yields starting from (
E)-nitro allylic alcohols, the crucial step being an inorganic base-catalyzed ...decarboxylative rearrangement of proposed labile unsaturated carbamates. A possible mechanism for the outcome of the reaction, characterized by the unusual retention of the sulfonyloxy group, is proposed.
Display omitted
A direct synthetic procedure to obtain chiral aziridines is reported, involving a diastereoselective aza-MIRC (Michael Initiated Ring Closure) reaction. Multifunctionalized aziridines are obtained in ...high overall yields (82–92%) and with a diastereomeric ratio up to 99:1. Further synthetic elaboration can lead to the formation of interesting biochemical molecules, such as amino glycosides. The diastereomeric induction seems to be strongly controlled both by the choice of chiral moiety and by the electron withdrawing groups (EWG) present on the starting alkenes.
Display omitted
Aza-MIRC (Michael-initiated ring closure) and C−H insertion products were obtained in the reactions of trifluoromethylated olefins with different nosyloxycarbamates by changing base and solvent. ...Aza-Michael addition products were not isolated. The presence and the position of the trifluoromethyl group allow control of the outcome of the reactions.
Short malonyl dehydro peptides have been epoxidized using H
2O
2/Na
2WO
4 dihydrate. The obtained diastereomeric epoxides were separated by HPLC and successfully tested in the ring opening reaction ...with
N-Boc
l-cysteine methyl ester, to indicate their electrophilic behavior. Moreover, by a simple two-step reaction, the epoxy malonyl peptides can be converted into the corresponding aziridino malonyl peptides.
Display omitted
(±)-2,2′-Dinitro-2,2′-biaziridines were obtained by a direct aza-MIRC (Michael initiated ring closure) reaction on (E,E)-1,4-dialkyl-2,3-dinitro-l,3-butadienes under very mild conditions. The ...reactions occur with high stereoselectivity as shown by the enantioselective HPLC analyses performed on the crude mixtures. Ring enlargement to 3,3′-bi(1,2,4-oxadiazole) derivatives was easily obtained by a simple treatment with sodium iodide in DMSO, with an unforeseen regioselective aziridine C−C cleavage.
The amination of 2-(trifluoromethyl)acrylates, performed by nosyloxycarbamates, gives two different aminated products, the derivatives of α-trifluoromethyl β-amino esters or the aziridines, in high ...yields by changing the reaction conditions. The aza-Michael addition product was isolated for the first time in this kind of reaction. This finding confirms the aza-MIRC mechanism we previously proposed. Asymmetric induction was also pursued.
Non-symmetric disubstituted malonamides rAA-mGly-AA′, obtained from Meldrum's acid, were considered as methylene active compounds and a Knoevenagel condensation methodology was developed involving ...piperidine and activated 4 Å molecular sieves as catalysts. The reaction is efficient, broad in scope, and easy to perform and allows access to E/Z mixtures of short malonyl dehydro peptides (MDHPs) rAA-mΔ²AA″-AA′, partially modified retro peptides characterized by an interesting combination of retro and dehydro modifications in the same structure.
Starting from a library of 2-
l-α-amino acyl (
E)-acrylonitriles, different short 2-cyano and 2-amido aziridinyl peptides, potential protease inhibitors, were obtained under parallel solution-phase ...conditions. The transformations include careful selection of conditions for aziridine deprotection and cyano group partial hydrolysis.
Starting from a library of 2-
l-α-amino acyl (
E)-acrylonitriles, different short 2-cyano and 2-amido aziridinyl peptides, potential protease inhibitors, were obtained under parallel solution-phase conditions. The transformations include careful selection of conditions for aziridine deprotection and cyano group partial hydrolysis.
Display omitted
PDF