Paolo Quadrelli

Copper (II) in organic synthesis. XI. Evaluation of the ligand architecture on the efficiency of a copper (II) catalyst for enantioselective Michael reactions

Abstract Several bis-copper (II) complexes with chiral ligands derived from 2-substituted 2-(salicylideneamino) ethanols have been tested as catalysts of enantioselective Michael reactions. The degree of enantioselection is strongly affected by the architecture of the ligand. The best result (75% e.e.) was obtained for a ligand having a substituent potentially suitable to induce the formation of a bis-tetradentate copper (II) complex with a square pyramidal coordination.

Copper(II) in organic synthesis. VIII enantioselective michael reactions with chiral copper(II) complexes as catalysts

Abstract - Using copper(II) chiral complexes as catalysts, enantioselective Michael reactions were performed. The degree of enantioselectivity depended on the design of the catalyst and the best results (70% e.e.) were obtained with tetradentate ligands.

Iminium Ions as Dienophiles in Aza‐Diels–Alder Reactions: A Closer Look

This review highlights the state of the art of the use of iminium ions as dienophiles in Aza-Diels-Alder (ADA) cycloadditions. An historical survey spanning the very first discovery of the reaction to modern developments, mechanistic studies and synthetic applications of the iminium variant of the ADA (iADA) reaction are presented. The discussion is focused on the intermolecular and intramolecular versions of the iADA reactions that are conducted in aqueous solutions to generate, in situ, the reactive dienophile from an amine hydrochloride and either aliphatic or aromatic aldehydes in the presence of a variety of dienes. The retro-ADA reaction is also presented as an interesting method for the protection of amines. The use of Lewis acid catalysis in these reactions was thoroughly studied by the reactions of different amines and aldehydes conducted in the presence of lanthanide(III) complexes.

A PHOTOCHEMICAL GENERATION OF NITROSOCARBONYL INTERMEDIATES

Abstract Nitroscarbonyl intermediates are photochemically generated from 1,2,4-oxadiazole-4-oxides and efficiently trapped with enes and dienes.

Cycloadditions of Nitrile Oxides to the Highly Reactive N-Acyl-2-oxa-3-azanorborn-5-enes Afford Versatile Cycloadducts and a Convenient Entry to Highly Functionalized Derivatives

N-Acyl-2-oxa-3-azanorborn-5-enes are highly reactive dipolarophiles in cycloadditions with nitrile oxides. The cycloadducts can be easily elaborated to various functionalized structures that are not directly accessible by 1,3-dipolar cycloadditions.

A mild oxidation of nitrile oxides: A new synthetic route to nitroso carbonyl intermediates

Abstract Addition of N-methyl morpholine N-oxide (NMO) to a nitrile oxide solution in dichloromethane at room temperature in the presence of a diene affords nitroso carbonyl adducts in fair yields.

A soluble polymer-bound Evans’ chiral auxiliary: synthesis, characterization and use in cycloaddition reactions

Abstract The synthesis of novel soluble polymer-supported optically-active oxazolidinone (Evans’ chiral auxiliary) with different chiral monomer/styrene ratios is described. The polymer was obtained in high yields and then functionalized with trans -crotonic anhydride to give a high loading polymer (2.42 mmol/g). The reactivity was tested in the 1,3-dipolar cycloaddition with diphenylnitrone under catalyzed and uncatalyzed conditions. The cycloadducts could be obtained in high purities and fair yields after reductive cleavage. The stereoselectivity is parallel to that obtained with the model substrate under classical solution conditions.

Cycloadditions of nitrile oxides to amidoximes. A general synthesis of 3,5-disubstituted 1,2,4-oxadiazole-4-oxides.

Abstract The cycloaddition of nitrile oxides to amidoximes is a general method for the sinthesis of 3,5-disubstituted 1,2,4-oxadiazole-4-oxides with the same or different substituents. The yields are only moderate since an equivalent amount of the nitrile oxide is consumed by reaction with the amine released in the fragmentation of the primary cycloadducts and reforms the amidoxime. With excess nitrile oxides the 1,2,4-oxadiazole-4-oxides undergo a disproportionation reaction to yield nitroso carbonyl intermediates and 1,2,4-oxadiazoles.

Merging and bifurcation of 4+2 and 2+4 cycloaddition modes in the archetypal dimerization of butadiene. A case of competing bispericyclic, pericyclic and diradical paths

The dimerization of butadiene has been explored by using DFT methods at the B3LYP level with the 6-311+G** basis set. A concerted bispericyclic TS for the endo pathway and a concerted pericyclic TS for the exo pathway are the lowest passes for the dimerization and occur at almost the same energy thus accounting for the lack of stereochemical preferences in the dimerization. Diradical paths involving two unswitched transoid butadiene moieties are competing and account for the formation of minor amounts of trans-1,2-divinyl cyclobutane and 1,5-cycloctadiene.

High-pressure behavior of methylammonium lead iodide (MAPbI3) hybrid perovskite

In this paper we provide an accurate high-pressure structural and optical study of MAPbI3 hybrid perovskite. Structural data show the presence of a phase transition towards an orthorhombic structure around 0.3 GPa followed by full amorphization of the system above 3 GPa. After releasing pressure the systems keeps the high-pressure orthorhombic phase. The occurrence of these structural transitions is further confirmed by pressure induced variations of the photoluminescence signal at high pressure. These variations clearly indicate that the bandgap value and the electronic structure of MAPI change across the phase transition.