Search results for "nucleophilic addition"

1,4-Benzoquinones with Styryl Substituents

2002

2-Styryl-1,4-benzoquinone (1) and compounds 2 and 3 containing 1 as a substructure all proved to be highly reactive towards thermal or photochemical [4π + 2π] cyclodimerization reactions. Chemo-, regio- and stereoselective processes lead to dimers (compounds 1−10), which can undergo secondary reactions consisting of the addition of nucleophiles combined with a twofold keto-enol tautomerism (10 ⇄ 12). An alternative process is dehydrogenation/oxidation followed by an intramolecular [4π + 2π] cycloaddition (10 ⇄ 11). The same selective [4π + 2π] cyclodimerization can be observed in solution upon irradiation (e.g., 1a ⇄ 10a), in contrast to irradiation in the crystalline state which yields a […

Synthesis ofN-Tosylguanidinesby Ring Cleavage of 1,2-Dihydro-2-tosyliminopyrimidines

2003

The present communication discloses a new synthetic method for the preparation of N-tosylguanidines in high yields by ring cleavage of 1,2-dihydro-2-tosyliminopyrimidines with methyl- amine.

Homochiral oxazolidin-2-ones and imidazolidin-2-ones by tandem nucleophilic addition–conjugate addition

2004

Abstract Treatment of both primary alcohols 1a , b and secondary amines 1c , d , tethered to a Michael acceptor with ( R )-phenylethyl isocyanate in the presence of DBU gave in good yield and high stereoselection diastereomeric mixtures of oxazolidin-2-ones 2a , b and 3a , b and imidazolidin-2-ones 2c , d and 3c , d , respectively. The cyclisation reaction was studied computationally by ab initio quantum mechanical methods. The observed stereoselectivity was explained on the basis of the different stability of both anions and transition states leading to 2a and 3a , respectively. The usefulness of the method was proven by conversion of 2a into the enantiomerically pure bioactive amino acid …

A DFT study of the domino reactions between imidazole NHC, ketenimines and DMAD or MP acetylene derivatives yielding spiro-pyrroles

2014

Abstract The domino reactions of imidazole carbene 9, ketenimine 10 and DMAD 5 or MP 7 to yield the formal [3+2] cycloadducts 12 or 14 have been investigated using DFT methods at the B3LYP/6-31G* level. These domino reactions are initialized by the nucleophilic attack of imidazole 9 on ketenimine 10 to yield the zwitterionic intermediate 11. The second reaction is a formal [3+2] cycloaddition (32CA) reaction between the zwitterionic intermediate 11 and acetylene carboxylates DMAD 5 or MP 7 yielding spiro-pyrroles 12 and 14. These formal 32CA reactions are initialized by the nucleophilic attack of the N3 nitrogen of intermediate 11 on the most electrophilic centres of these acetylene derivat…

Enantioselective copper-aminopyridine-catalyzed aza-Henry reaction with chelating N-(2-pyridyl)sulfonyl imines

2012

This article describes a copper-catalyzed aza-Henry reaction. Copper complexes of camphor-derived aminopyridines catalyze the addition of nitromethane to N-(2-pyridyl)sulfonyl aldimines to give the corresponding β-nitrosulfonamides with good yields and variable enantiomeric excesses (up to 83%). An example of transformation of these compounds into N-(2-pyridyl)sulfonyl-α-amino acids and deprotection of the sulfonamide with Mg–MeOH is provided. Chirality 24:441–450, 2012. © 2012 Wiley Periodicals, Inc.

Stereoselective Nucleophilic Addition Reactions of Reactive Pseudopeptides

1992

ELABORATION OF CURCUMIN INTO DIKETONE MODIFIED ANALOGUES DEVOID OF NUCLEOPHILIC ADDITION CAPABILITY; IMPLICATIONS FOR THEIR ANTITUMOR AND CHEMOSENSIT…

2009

Curcumin (CUR), a polyphenolic compound extracted from Curcuma longa L.,can beconsidered as a good lead compound for the design of new drugs for the treatment of cancer and other therapeutic purposes. CUR is endowed with a diketone function, which appears to be important for its antitumor activity: also depending on the dose, the compound may show complex either pro-oxidant or anti-oxidant effects, which both may, at least in part, be linked to this structural moiety. In the lower concentration, "chemopreventive", range, CUR behaves mainly as an antioxidant; at higher concentrations, the a, b-unsaturated 1,3-diketone, as a Michael acceptor, can form adducts with the –SH groups and generate …

Sunlight-induced functionalisation reactions of heteroaromatic bases with aldehydes in the presence of TiO2: A hypothesis on the mechanism

2007

In previous studies we reported a new photocatalytic system involving polycrystalline TiO2 for the selective functionalisation of heteroaromatic bases with ethers and amides. In order to extend the applications of this new reaction and to better understand the mechanism involved, we have examined aromatic and aliphatic aldehydes as acyl radical sources for the nucleophilic addition to protonated N-heteroarenes in acetonitrile as the solvent and TiO2/H2O2 as the photocatalytic system. Acyl radicals may undergo decarbonylation to yield the corresponding alkyl radicals. Acyl/alkyl derivative ratios depend on the nature of the aldehydes, and present a different distribution from that obtained i…

EPR spectroscopic characterization of persistent germyl-substituted Pb(III)- and Sn(III)-radicals.

2010

In this report we present the synthesis and the detailed electron paramagnetic resonance (EPR) spectroscopic characterization of novel trivalent lead- and tin-based radicals comprising sterically demanding germyl substituents. The investigated radicals are derived from the recently reported trihypersilyl-substituted tetryl radicals *PbHyp3 and *SnHyp3. The tetryl radicals *Pb(Ge(SiMe3)3)3 (8), *Pb(Ge(SiMe3)3)2Si(SiMe3)3 (9), *PbGe(SiMe3)3(Si(SiMe3)3)2 (10), and *Sn(Ge(SiMe3)3)3 (11) show substitution patterns derived from stepwise (9, 10) or complete (8, 11) substitution of hypersilyl groups (Hyp = Si(SiMe3)3) in *PbHyp3 and *SnHyp3 by homologous hypergermyl groups (Hge = Ge(SiMe3)3). They …

Diastereoselective synthesis of 2-phenyl-3-(trifluoromethyl)piperazines as building blocks for drug discovery.

2014

The synthesis of enantiomerically pure cis- and trans-2-phenyl-3-(trifluoromethyl)piperazines is described. It involved, as the key step, a diastereoselective nucleophilic addition of the Ruppert-Prakash reagent (TMSCF3) to alpha-amino sulfinylimines bearing Ellman's auxiliary. This methodology allows an entry into hitherto unknown trifluoromethylated and stereochemically defined piperazines, key scaffold components in medicinal chemistry.