Pier Paolo Piras

Stereocontrolled synthesis and functionalization of cyclobutanes and cyclobutanones.

In the last decade a certain number of new cyclobutane and cyclobutanone synthesis and functionalization protocols have been published. Organo- and biocatalyzed eco-friendly approaches to cyclobutane-containing molecules have been developed with interesting results. Also, successful new total synthesis of bioactive compounds and drugs have been recently reported where a four membered ring represented the key intermediate. Therefore, the rising interest in this field represents a great point of discussion for the scientific community, disclosing the synthetic potential of strained four membered ring carbocyclic compounds. Herein we report a critical survey on the literature concerning the enantiocontrolled synthesis and functionalization of cyclobutane derivatives, with particular attention to metal-free, low impact methodologies, published during the period 2000–2013.

Very high stereoselectivity in organocatalyzed desymmetrizing aldol reactions of 3-substituted cyclobutanones

N-Phenylsulfonyl (S)-proline catalyzes the direct aldol reaction of 3-substituted cyclobutanones and aryl aldehydes in good yield and with excellent diastereoselectivity and enantioselectivity. This desymmetrization process provides highly functionalized cyclobutanones with control over three contiguous stereogenic centers.

Regioselective palladium(0) catalyzed reduction of 1-alkenylcyclopropyl esters as equivalent of the wittig reaction §

Abstract Palladium(0) catalyzed reduction of 1-(1-alkenyl)- and 1-(1-cycloalkenyl)cyclopropyl esters provides an useful alternative to the Wittig reactions of cyclopropylidenetriphenylphosphorane or of cyclopropanone hemiacetals and an easy route to strained methylenecyclopropane derivatives.

Catalytic enantioselective Amadori–Heyns rearrangement of racemic α-hydroxy ketones with arylamines: synthesis of optically active α-arylamino ketones

A novel synthesis of optically active α-arylamino ketones through an organocatalytic enantioselective Amadori-Heyns rearrangement is described.

Synthesis of Tertiary Cyclobutanols through Stereoselective Ring Expansion of Oxaspiropentanes Induced by Grignard Reagents

Abstract The stereoselectivity of the ring expansion of oxaspiropentanes to cyclobutanols induced by Grignard reagents has been studied. It has been found that the reaction occurs through the intermediacy of a cyclobutanone, formed stereospecifically, whereas the attack of the Grignard reagent on the carbonyl group of the cyclobutanone is stereospecific only in the case of the oxaspiropentanes derived from aldehydes.

Palladium (0) Catalyzed Nucleophilic Substitution On 2-Cyclopropylidene-phenoxy Ethanes

Abstract 2-cyclopropylidene-phenoxy ethanes 5, 2-substituted with alkyl, aryl or heterocyclic groups are readily obtained in high yields by the Wittig reaction of the easily accessible α-phenoxy etanones 4 with (3-bromo propyl) triphenylphosphonium bromide. They react with complete regioselectivity in palladium (0) catalyzed nucleophilic substitutions with a series of soft carbon nucleophiles giving an easy entry to 5,6-methanoamino acids.

Tetrazole amides as hydrogen-bonding donor catalysts in the chemoselective oxidation of sulphides and disulphides

The oxidation of organosulphides catalyzed by hydrogen bonding donors deriving from aminotetrazole has been studied. The oxidation reaction was performed in CH2Cl2 solution using TBHP (1.1 eq.) as a versatile and chemoselective new catalyst to sulfoxides. 5 mol.% catalyst loading afforded organosulfoxides with complete conversion and yields around 90–95%. Tetrazole amide derivatives can be easily recovered by simple filtration and reused several times. Reactions were carried out in scales ranging between mg and multigram in order to test the robustness of the process. 1H-NMR studies and DFT calculations were exploited to disclose the role of tetrazole amide–TBHP complexes in the sulphides oxidation reaction as new performing catalysts.

New aminotetrazole derivatives as hydrogen bonding catalysts. A green and selective oxidation of organosulphides with H2O2 in H2O

The oxidation of organosulphides catalysed by hydrogen bonding donors derived from aminotetrazole has been studied. The oxidation reaction was performed in a H2O solution using H2O2 as a versatile, green and chemoselective new approach to sulphoxides. Sulphoxide compounds are obtained in high yields and excellent selectivity through a new and easy to perform oxidation protocol. Aminotetrazole derivatives can be recycled by filtration and reused several times without expensive purification procedures.

Mechanism of decarbalkoxylation of arylmethylene-propanedioic acid dimethyl esters

Abstract The decarbalkoxylation in DMSO-NaX-H2 O, of some arylmethylene propanedioic acid dimethyl esters is studied. Both the relative rates of the para (R = NO2, H, CH3, OCH3) and the ortho [R = H, OCH3 , OCH(CH3)2]substituted aryl derivatives, together with the stereochemical outcome, support a preliminary nucleophilic attack by water followed by decarbalkoxylative elimination.

A new entry to alkylidenecyclopropanes through a Ramberg-Backlund rearrangement of cyclopropylsulfones

Abstract The first use of the Ramberg-Backlund rearrangement of cyclopropylsulfones in the synthesis of alkylidenecyclopropanes is reported.