Search results for "Michael"

Il Polar prima del Polar: il poliziesco italo-americano tra fine Ottocento e gli anni Trenta del Novecento

2018

Tra la fine dell’Ottocento e gli anni Trenta del Novecento, alcuni Italiani immigrati negli Stati Uniti – quali, fra gli altri, Bernardino Ciambelli, Italo Stanco, Garibaldi Marto Lapolla, Louis Forgione, nonché il sodalizio letterario costituito da Michael Fiaschetti e Prosper Buranelli – si sono cimentati nel genere del poliziesco con alcuni testi che, partendo da alcune delle caratteristiche tipiche del Mystery, quali la serializzazione e l’incardinamento della fabula in uno specifico contesto urbano, insieme ad alcuni degli elementi caratteriali dei personaggi dell’Hard boiled non perdono mai di vista la peculiare ‘missione’ di denuncia politica, economica e sociale. Facendo del problem…

Polystyrene-supported organocatalysts for α-selenenylation and Michael reactions

2011

Abstract Three different resin-supported catalysts have been prepared by using the well established post-modification approach by means of thiol-ene coupling reaction. Two catalysts were tested for the first time in the asymmetric α-selenenylation of propanal, while the third catalyst was used in the Michael addition reaction. While the preliminary results are not encouraging in the case of supported Jorgensen’ catalyst, interesting data have been collected with both for the supported MacMillan and prolyl-prolinol catalysts. In fact, these catalysts displayed good activity and selectivity. A reversed enantioselectivity in the α-selenenylation was observed by changing the polarity of the sol…

Synthesis of Pyrrolidin-2-ones and of Staurosporine Aglycon (K-252c) by Intermolecular Michael Reaction

1999

Indolo[2,3-a]pyrrolo[3,4-c]carbazoles were isolated from nature, e.g., from low plants, especially fungi, as structurally rare natural substances. Responsible for naming and also the most important representative of this type is staurosporine (1), isolated from Streptomyces staurosporeus, and its aglycon (2), also known as staurosporinone or K-252c. 3,4-Disubstituted pyrrolidin-2-ones, a group of compounds with many interesting biological properties are related to staurosporinone. The most important property is the inhibition of protein kinase C (PKC), so that this antiproliferative agent can interfere with the cell cycle. The synthetic strategy, developed by us, allows the synthesis of pyr…

Organocatalytic Enantioselective 1,6-aza -Michael Addition of Isoxazolin-5-ones to p -Quinone Methides

2020

N-sulfinyl amines as a nitrogen source in the asymmetric intramolecular aza-Michael reaction: total synthesis of (-)-pinidinol.

2010

N-Sulfinyl amines have been successfully employed as nitrogen nucleophiles for the asymmetric intramolecular aza-Michael reaction. The synthetic strategy involves a cross-metathesis reaction followed by the Michael-type cyclization, either in a base-catalyzed two-step procedure or in a tandem fashion. The developed methodology allows access to chiral substituted pyrrolidines and piperidines bearing one or two stereocenters and it has been applied to the synthesis of the piperidine alkaloid (-)-pinidinol.

Diastereoselective Michael Addition of (S)-Mandelic Acid Enolate to Nitroalkenes. Enantioselective Synthesis of α-Hydroxy-α,β-diaryl-γ-lactams.

2004

Abstract The reaction of the lithium enolate of the ( S , S )- cis -1,3-dioxolan-4-one derived from optically active ( S )-mandelic acid and pivalaldehyde with several aromatic nitroalkenes in the presence of HMPA proceeds readily to give the corresponding Michael adducts in good yields and diastereoselectivities. Reduction of the nitro group with Zn/HCl/EtOH/H 2 O with concomitant intramolecular aminolysis of the acetal moiety leads directly to enantiomerically pure α-hydroxy-α,β-diaryl-γ-lactams.

The role of fluorine in the stereoselective tandem Aza-Michael addition to acrylamide acceptors: An experimental and theoretical mechanistic study

2007

Aza-Michael additions of alpha-amino esters to fluorinated acceptors take place in a highly stereoselective manner, to give partially modified Psi-[NHCH2]retropeptides incorporating a hydrolytically stable trifluoroalanine mimic. The reaction mechanism has been investigated experimentally and theoretically, in order to explain the effect of the trifluoromethyl group on the reactivity and the origins of the experimentally observed stereocontrol. The reaction is a two-step process, involving a tandem aza-Michael addition followed by a stereoselective hydrogen transfer. Both steps are base-catalyzed. The high level of stereocontrol is the result of a combination of electrostatic interactions a…

A theoretical study of carbon-carbon bond formation by a Michael-type addition.

2012

A theoretical study of the Michael-type addition of 1,3-dicarbonyl compounds to α,β-unsaturated carbonyl compounds has been performed in the gas phase by means of the AM1 semiempirical method and by density functional theory (DFT) calculations within the B3LYP and M06-2X hybrid functionals. A molecular model has been selected to mimic the role of a base, which is traditionally used as a catalyst in Michael reactions, an acetate moiety to modulate its basicity, and point charges to imitate the stabilization of the negative charge developed in the substrate during the reaction when taking place in enzymatic environments. Results of the study of six different reactions obtained at the three di…

Crystal structure of ethyl 2-(di-eth-oxy-phosphor-yl)-2-(2,3,4-tri-meth-oxy-phen-yl)acetate.

2014

The title compound, C17H27O8P, was prepared by Michaelis–Arbuzov reaction of ethyl 2-bromo-2-(2,3,4-trimethoxyphenyl)acetate and triethyl phosphite. Such compounds rarely crystallize, but single crystals were recovered after the initial oil was left for approximately 10 years. The bond angle of thesp3-hybridized C atom connecting the benzene derivative with the phospho unit is widened marginally [112.5 (2)°]. The terminal P—O bond length of 1.464 (2) Å clearly indicates a double bond, whereas the two O atoms of the ethoxy groups connected to the phosphorous atom have bond lengths of 1.580 (2) Å and 1.581 (3) Å. The three methoxy groups emerge out of the benzene-ring plane due to steric hind…

Stereocontrol in Diphenylprolinol Silyl Ether Catalyzed Michael Additions : Steric Shielding or Curtin-Hammett Scenario?

2017

The enantioselectivity of amine-catalyzed reactions of aldehydes with electrophiles is often explained by simple steric arguments emphasizing the role of the bulky group of the catalyst that prevents the approach of the electrophile from the more hindered side. This standard steric shielding model has recently been challenged by the discovery of stable downstream intermediates, which appear to be involved in the rate-determining step of the catalytic cycle. The alternative model, referred to as Curtin-Hammett scenario of stereocontrol, assumes that the enantioselectivity is related to the stability and reactivity of downstream intermediates. In our present computational study, we examine th…