Arrigo Forni

On the effect of ring substituents in the carbonylation of aziridines

Abstract The effect of ring substituents on the cobalt carbonyl-catalyzed carbonylation of functionalized aziridines to β-lactams has been investigated. A variety of aziridines with different substituents and stereochemistry has been synthesized and subjected to carbonylation. The ring expansion to β-lactam takes place in the absence of an electron-withdrawing substituent and higher yields are always obtained for cis-aziridines. Moreover, the regioselectivity of the reaction is affected by the nature of substituents at ring carbon atoms.

Stereoselective synthesis of fluorinated β-aminoacids from ethyl trans-N-benzyl-3-trifluoromethylaziridine-2-carboxylate

Abstract trans-N-Benzyl-3-trifluoromethyl-2-ethoxycarbonylaziridine 2a, easily obtainable in enantiopure forms by CAL-catalysed enzymatic resolution, allowed the regio- and stereoselective synthesis of chiral fluorinated anti-α-functionalised-β-aminoacids, such as trifluoroisoserinates or trifluoro-β-alanine, and trans-3-halo- or 3-hydroxy-β-lactams. Starting from the enantiomerically pure methyl analogue of the title compound, 2c, pure enantiomers of trifluoroisoserine can be obtained in high overall chemical yield. Absolute configurations of optically active β-aminoacids were determined by chemical correlation.

(R)-(+) and (S)-(−) ethyl 4,4,4-trifluoro-3-hydroxy butanoate by enantioselective Baker’s yeast reduction

Abstract ( R )-(+) and ( S )-(−) ethyl 4,4,4-trifluoro-3-hydroxybutanoate are obtained both by enantioselective Baker’s yeast reduction of ethyl 4,4,4-trifluoro-3-oxobutanoate in the presence of allyl bromide or allyl alcohol. The two additives act as inhibitors of Si or Re yeast-enzymes, respectively.

Regioselectivity of ring-opening reactions of optically active N-acetyl-2-methoxycarbonylaziridine

Abstract (S)-(−)-N-acetyl-2-methoxycarbonylaziridine 1 undergoes easy ring-opening by Bronsted acids or nucleophiles in the presence of a Lewis acid catalyst. The regioselectivity is not always exclusive, affording optically active α- and β-aminoacids.

Stereochemical control in yeast reduction of fluorinated β-diketones

Abstract The presence of additives in bakers′ yeast reductions of fluorinated β-diketones turns the stereochemistry of the reaction towards the (R) or (S) enantiomers of the corresponding ketols.

Synthesis, enzymatic resolution and absolute configuration of ethyl trans-3-(trifluoromethyl)pyroglutamate

Abstract Ethyl trans -3-(trifluoromethyl)pyroglutamate 1 is synthesized in excellent yield; racemic 1 is enzymatically resolved with α-chymotrypsin-catalyzed hydrolysis affording both the enantiomerically pure enantiomers. The absolute configuration is established by X-ray analysis of the corresponding trichloroethylester.

Asymmetric synthesis and stereochemical properties of optically active n-sulphonyl-3-aryloxaziridines

Abstract Oxidation of prochiral sulphonimines (RSO 2 N=CHAr) with (1S)-(+)-PCA, followed by fractional crystallization of the crude reaction products, provides highly optically-pure N-sulphonyl-3-aryloxaziridines 1 H NMR spectra recorded in the presence of chiral solvent or shift reagent, CD spectra, and the results observed by using them as new chiral oxidizing reagents, are also reported.

Stereoselective synthesis and absolute configuration of (1′R,3R,4R)-4-acetoxy-3-(2′,2′,2′-trifluoro-1′-hydroxyethyl)azetidin-2-one

Abstract The title compound 3, an intermediate in the synthesis of fluorocarbapenems, is obtained with high stereocontrol by the condensation of (R)-(+)-ethyl 4,4,4-trifluoro-3-hydroxybutanoate with N-trimethylsilyl cinnamylidenimine. X-Ray diffraction analysis of the condensation product and chemical correlations allowed the unambiguous determination of the absolute configuration.

Enzymatic resolution of aziridine-carboxylates

Abstract N-acyl-aziridine-2-carboxylates and N-acyl-aziridine-2,3-dicarboxylates have been resolved with good to excellent stereochemical purity by enzymatic hydrolysis catalyzed by lipase from Candida cylindracea .

Biotransformations of fluorinated sulphenyl and sulphonyl compounds

Abstract optically active sulphenyl and sulphonyl fluorohydrins were obtained by reduction of ketones with bakers yeast or by enzymatic resolution of their racemic esters using Candida cylindracea lipase. Crystallization of partially optically active fluorohydrins gave enantiomerically pure forms. Enantioselectivity of the enzymatic reactions is affected by steric requirements of the substituents.