Giorgio Molteni

Cu/Cu-oxide nanoparticles as catalyst in the “click” azide–alkyne cycloaddition

Mixed Cu/Cu-oxide nanoparticles are an effective catalyst for the “click” 1,3-dipolar cycloaddition between azides and terminal alkynes, featuring short reaction times, soft reaction conditions and full regioselectivity.

MeOPEG-bounded azide cycloadditions to alkynyl dipolarophiles

Abstract The MeOPEG-supported azide 2 was reacted in the presence of a number of alkynyl dipolarophiles. The corresponding 1-MeOPEG-supported-1,2,3-triazoles were obtained in nearly quantitative yields. Acidic hydrolysis of the cycloadducts 5b and 6b caused the removal of the MeOPEG pendant giving 4-methoxycarbonyl-1,2,3-triazole 9 and 5-methoxycarbonyl-1,2,3-triazole 10 , respectively.

Asymmetric biomimetic oxidations of phenols: the mechanism of the diastereo- and enantioselective synthesis of dehydrodiconiferyl ferulate (DDF) and dehydrodiconiferyl alcohol (DDA)

Abstract Stereoselective bimolecular radical coupling of enantiopure phenylpropenoidic phenols are described, starting from enantiopure amidic derivatives of ferulic acid. The latter were prepared from ferulic acid by reaction with (S)-alanine or Oppolzer camphor sultam. The oxidation step was performed both enzymatically (HRP/H2O2) and chemically (Ag2O). The observed enantioselectivity in the oxidation step encompasses the range 65–84% and is consistent with the conformational analysis of the quinone methide intermediates at the PM3 level.

A facile synthesis of flumazenil analogues

Abstract A number of 8-substituted 5-methyl[1,2,3]triazolo[1,5-a][1,4] benzodiazepin-6(4H)-ones (6) were synthesised in a concise and efficient way starting from isatoic anhydrides and exploiting an intramolecular azide cycloaddition.

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.

1,3-Dipolar cycloadditions in aqueous media

1,3-Dipolar cycloadditions in aqueous media represents a useful, non conventional protocol in the synthesis of a variety of five-membered heterocycles. In addition, water as the solvent may significantly enhance cycloaddition rates and/or stereoslectivities. The literature data on this subject are reviewed in a systematic way, with an emphasis to improvements with respect to cycloadditions performed in the usual, non-aqueous conditions.

Uncommon aqueous media for nitrilimine cycloadditions. I. Synthetic and mechanistic aspects in the formation of 1-aryl-5-substituted-4,5-dihydropyrazoles

A number of 1-aryl-5-substituted-4,5-dihydropyrazoles 4 have been synthesised by 1,3-dipolar cycloaddition of variously substituted nitrilimines 2 onto the appropriate alkenyl dipolarophiles 3 in aqueous media and in the presence of a surfactant. Under these conditions, uncommon for the large majority of [3 + 2] cycloadditions, the electronic features of both the cycloaddends strongly dictate the reaction outcome. Clean and fast cycloadditions were observed between electron-rich nitrilimines and electron-poor dipolarophiles, while the reversal of the electronic features of the reactants gave poor results. Changes in surfactant concentration leads to some novel mechanistic insights.

Diastereoselective synthesis of bis(3,5)pyrazolophanes by sequential inter- and intramolecular cycloadditions of homochiral nitrilimines

Abstract Starting from ethyl ( S )-lactate as the chiral unit, we have developed the synthesis of the enantiopure bis(3,5)pyrazolophanes 9 and 19 by means of sequential inter- and intramolecular cycloadditions of nitrilimine intermediates.

The first case of asymmetric induction in intramolecular nitrile imine cycloadditions: synthesis of enantiopure 3-substituted 6-oxo-2,3,3a,5-tetrahydro-4-carbomethoxy-furo[3,4-c]pyrazoles

Abstract Intramolecular cycloaddition of homochiral nitrile imines 5 , generated in situ from base treatment of the corresponding hydrazonoyl chlorides 4 , involves diastereoselective formation of the title compounds in the enantiomerically pure form.

Stereoselective intramolecular cycloadditions of homochiral nitrile imines: synthesis of enantiomerically pure 3,3a-dihydro-pyrazolo[1,5-a][1,4]benzodiazepine-6(4H)-ones

Abstract Starting from the commercially available ( S )-1-phenylethylamine, we have synthesised the homochiral hydrazonoyl chlorides 4 . The intramolecular cycloaddition of the corresponding nitrile imines 5 gave the diastereoisomeric 3,3a-dihydro-pyrazolo[1,5- a ][1,4]benzodiazepine-6(4 H )-ones 6 and 7 in enantiopure form.