Rosanna Bernardi

Nucleophilic character of alkyl radicals—VI : A new convenient selective alkylation of heteroaromatic bases

Abstract A new method of homolytic alkylation of heteroaromatic bases is described, in which the silver-catalysed oxidative decarboxylation of acids by peroxydisulphate is used as a source of alkyl radicals. The method is particularly noteworthy because of the good yields and the high selectivity obtained, due to the nucleophilic character of the alkyl radicals; for synthetic interest it is comparable to electrophilic alkylation in the homocyclic series.

On the steric course of addition of Grignard reagents onto α,β-dialkoxy erythro and threo chiral aldehydes. Synthesis of (+) and (−)-exo and endo-brevicomin

Addition of BrMgCH2CH3 onto the erythro and threo aldehydes (1) and (2) to form (3)+(6) and (9)+(10) proceeds with 6:4 and 8:2 threo-erythro selectivity, respectively. From (3) and (6), (2S) and (2R)-2-benzyloxy butyraldehyde (13) and (14) have been prepared. Addition of onto (13) and (14) proceeds with 6:4, threo-erythro selectivity, to give after preparative gas chromatographic separation, the enantiomeric forms of exo- and endo- brevicomin (19), (21) and (20), (22).

Trifluoromethyl vs. methyl ability to direct enantioselection in microbial reduction of carbonyl substrates.

Abstract The stereoselective reduction of 3-trifluoromethylcyclohexanone ( 1a ), ( E )-1,1,1-trifluoro-4-phenyl-3-buten-2-one ( 3a ), and their unfluorinated analogues 1b and 3b has been performed with some growing microorganisms. Differences in the electronic and steric properties of the trifluoromethyl and methyl residues result in different chemo- and stereoselectivities in the microbial reduction of phenylbutenones 3a and 3b while cyclohexanones 1a and 1b showed strictly similar stereoselectivities. A new protocol based on 13 C NMR spectra of 2-phenylpropionic acid esters has been used to assign the absolute configuration of the obtained secondary alcohols.

Nucleophilic character of alkyl radicals generated in redox processes—I : Reactivity of the 5-(methoxycarbonyl)-pentyl radical towards conjugated olefins

Abstract New syntheses of polyfunctional long-chain compounds were performed by alternating free radical additions of 5-(methoxycarbonyl)-pentyl radical to pails of conjugated olefins. Copolymerization was avoided by a metal salt redox system, which selectively oxidizes the radicals involved. Quantitative data of relative reactivities towards α-methylstyrene, acrylic acid, methyl acrylate, acrylonitrile and maleic anhydride emphasize the nucleophilic character of the 5-(methoxycarbonyl)-pentyl radical. Theoretical and synthetic aspects are discussed.

Formation of the (R)- and (S)-enantiomers of ethyl 3-hydroxybutanoate and of 1-(1,3-dithian-2-yl)-2-hydroxypropane by microbial reduction

The (R)and (S) enantiomers of 3-hydroxybutanoate [(2a) or (3a)] and 1-(1,3-dithian-2-yl)-2-hydroxypropane [(2b) or (3b)] are obtained from ethyl 3-oxobutanoate (1a) and 1-(1,3-dithian-2-yl)-2-oxopropane (1b), respectively, using growing cultures from different strains of Geotrichum candidum and Aspergillus niger.

Photoinitiated substitution reactions of 2 and 4-pyridinecarbonitrile with cyclopentene

Abstract The photoreactions of 4 and 2-pyridinecarbonitrile with cyclopentene carried out in acetone or in acetonitrile solutions lead, respectively, to 4-(2 cyclopentenyl)-pyridine 1 and 2-(2 cyclopentenyl)pyridine 2 . From 2-pyridinecarbonitrile a little amount of ketone 3 is obtained.

Photochemically induced electron transfer from aniline derivatives to pyridine-2,4-dicarbonitrile: synthetic and mechanistic aspects

A study on the photochemically induced electron transfer from substituted aniline donors to a 2,4-dicyanopyridine acceptor permits the synthesis of new amino derivatives of the pyridine and forms the basis of a hypothesis on the mechanism of the reaction and the influence of the substituent on the aniline ring.

Photoinitiated substitution reactions of heterocyclic bases: reaction with alkenes

A method is described for the synthesis of allyl heterocyclic bases by a photoinduced substitution reaction of cyanoheterocyclic bases and certain alkenes.

A study of the photochemically induced reaction of pyridine-2,4-dicarbonitrile with primary and secondary amines. A direct synthesis of aminocyano-pyridines

A novel synthesis of alkylaminopyridinecarbonitriles by a photoinitiated substitution reaction between pyridine-2,4-dicarbonitrile and certain amines is described. The mechanism is discussed.

Regiochemical control in the allylic hydrogen abstraction from 1-X-substituted cyclohexenes.

Abstract Allylic hydrogen abstraction is strongly affected by substituents attached to the double bond. Evidence regarding this regiochemical control is presented for the first time.