Paola Del Buttero

Tricarbonyl(η6arene)Chromium(0) complexes as chiral auxiliaries: Asymmetric synthesis of β-aminoesters and β-lactams by Reformatsky condensation

Abstract Highly stereoselective syntheses (e.e. > 98%) of β-aminoesters and β-lactams were accomplished using enantiomerically pure tricarbonyl (η6benzaldimine)chromium complexes in a Reformatsky type reaction promoted by ultrasound. A correlation between the configuration of complexed imines and absolute configuration of β-lactam derivatives is reported.

The first chiral racemic Fischer-type aminocarbene complex bearing a C2 symmetry amine: stereochemical characteristics and application to Michael addition reactions

Abstract The synthesis of [ trans -methyl(2,6-dimethyl)morpholinocarbene]pentacarbonylchromium(0) complex ( 3 ) is reported, together with the stereoselective Michael addition of the conjugate base of complex 3 to enones.

Stereoselective synthesis of a new enantiopure tricyclic β-lactam derivative via a tricarbonyl(η6-arene)chromium(0) complex

Abstract The tricyclic β-lactam 5 has been synthesized both in racemic and enantiopure form starting from the enantiomerically pure tricarbonylchromium(0) complex 1. The synthetic sequence involves the stereoselective [2+2] cycloaddition of 1 with acetoxyacetylketene, followed by intramolecular aromatic nucleophilic substitution of the fluorine atom. Mechanistic pathways leading to 5 are discussed.

Stereoselective synthesis of β-sultams using chiral tricarbonyl(η6-arene)chromium(0) complexes

Abstract The reaction of (−)1R or (+)-1S-tricarbonyl(2-substituted benzaldehyde)chromium complexes with tertbutylmethanesulfonamide dianion afforded, after decomplexation and intramolecular cyclization, the enantiomerically pure N-tert-butyl-3-(2-phenyl substituted)-1,2-thiazetidine 1,1 dioxide derivatives. The hydrolytic ring opening gave the corresponding enantiopure β-aminosulfonic acid.

Tricarbonyl(η6arene)chromium(0) complexes as chiral auxiliaries. Homochiralβ-lactams synthesis “via” [2+2] cycloaddition reaction.

Abstract A highly enantioselective synthesis of β-lactams “via” a [2+2] cycloaddition reaction of homochiral tricarbonyl [ N -(2-methoxybenzylidene)aniline]chromium with ketenes is reported. Moreover the reaction of (+)-( 1 S)-tricarbonyl[4-methoxy- N -(2-methoxy cinnamylidene)aniline]chromium with acetoxy ketene gives the corresponding 4-styryl-β-lactam in good yield but with moderate stereoselection.

Stereoselective alkynylation of chiral benzaldehyde chromium tricarbonyl complexes. Synthesis of optically active alkynyl alcohols

Abstract Addition of lithium acetylides and ethynyl magnesium bromide to chiral ortho substituted benzaldehyde tricarbonylchromium complexes 1 – 3 gives alkynyl alcohols 4 – 7 in good yields and with complete stereoselection.

Asymmetric darzens condensation on chiral η6Cr(CO)3 complexed benzaldehydes

Abstract Enantioselective Darzens condensation has been achieved from optically active ortho substituted benzaldehyde(tricarbonyl)chromium complexes. The enantiomeric excesses were very high with 2-methoxy and 2-chloro benzaldehyde(tricarbonyl)chromium and the corresponding epoxides obtained were nearly optically pure.

The intramolecular aromatic nucleophilic substitution as a route to tricyclic β-lactams. Synthesis of the novel 4-oxa-7-azabicyclo[4.2.0]octane skeleton

Sodium borohydride-carbonyl reduction of the novel 3-(2-fluoro-5-nitro) phenyl-4-benzoyl-2-azetidinones 3 and 7 gave quantitatively the stereoisomeric carbinols (4R p ,5S p )-4 and (4R p ,5R p )-5. Treatment of the latter with sodium hydride gave the title compounds 8 and 9, respectively, with good overall yield. The rationale of the stereochemical relationships outlined in the sequences 3 (or 7)!4!8 and 3 (or 7)!5!9 is given according to the conformational and keto-enol equilibria of the reactant(s). q 2003 Elsevier Science Ltd. All rights reserved.

Novel fluorinated amino-stilbenes and their solid-state photodimerization

We synthesized a series of polyfluoro-amino-stilbenes in satisfactory yields by Wittig reaction of 4-piperazinyl-benzalhehydes with pentafluoro-benzylidene-triphenyl-phosphorane and we analyzed the photochemical behavior of these stilbenes in the solid state; thanks to arene–perfluoroarene π–π interactions, some of them have shown a good propensity to give the corresponding cyclobutane photodimers in quantitative yields. The photocyclization is reversible both in solution and in polymeric matrix, affording the corresponding stilbenes with different cis–trans stereo-selectivity.

Stereoselective intramolecular 1,3-dipolar cycloaddition of chiral chromium tricarbonyl complexed nitrone

Abstract The new tricarbonyl(2-allyloxybenzaldehyde)chromium(0) complex ( 4a ) has been prepared in both a racemic and an enantiomerically pure form. The thermal intramolecular 1,3-dipolar cycloaddition of the corresponding (1 R )-N-methyl nitrone ( 5a ) afforded, after decomplexation, cis -(3a S ,9b R )-1,3a,4,9b-tetrahydro-1-methyl-3H-[1]benzopyrano[4,3-c]isoxa zole ( 7 ) with complete enantioselection.