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Andrei K Yudin

Publications and source records attributed to Andrei K Yudin.

At least 19 recordsLinked to original sources
PubMed2006

Palladium-catalyzed oxidative activation of arylcyclopropanes.

Palladium chloride-catalyzed intramolecular activation of electroneutral cyclopropane derivatives results in cleavage of the cyclopropane ring followed by formation of heterocyclic derivatives. Phenols, carboxylic acids, and amide groups were considered as substituents ortho to the cyclopropane ring in this catalytic activation chemistry. The regioselectivity observed in the case of amide-containing substrates was different from that of carboxylic acid-containing substrates, ruling out simple cyclopropane isomerization followed by a Wacker oxidation as the mechanistic pathway. [reaction: see text]

Amides↗
PubMed2006

Readily available unprotected amino aldehydes.

We report a new class of bench-stable compounds that contain seemingly incompatible functional groups: an aldehyde and an unprotected secondary amine. The thermodynamic driving force to undergo condensation between these two functionalities is offset by a high barrier imposed on this process by the aziridine ring strain. The resulting amino aldehydes exist as dimers and in the solid state. They are stable to epimerization and contain two orthogonal reaction centers, namely, an amine/aziridine and an aldehyde. Their ability to act as linchpins has been evaluated in complex heterocycle synthesis. For instance, pentacyclic frameworks can be made in one simple operation using N-benzyltryptamine as the reaction partner. Construction of other molecular skeletons with minimal use of protecting group manipulations should be feasible.

Journal Article↗
PubMed2006

Rhodium-catalyzed stereoselective formation of Z-enamines from allylaziridines.

Rhodium (I)-catalyzed isomerization of N-allylaziridines affords isolable Z-enamines in excellent yields and with high stereoselectivity. Cationic [Rh(BINAP)(COD)]OTf and RhH(CO)(PPh3)3 follow the same selectivity toward the Z-isomers. This selectivity is not observed with other N-allylamines which give the thermodynamically more stable E-isomers. These unexpected results suggest a possible deviation from the commonly accepted mechanism of isomerization. Preliminary results show that the Z-enamines undergo cycloaddition with DMAD to form highly strained N-cyclobutenyl aziridines.

Allyl Compounds↗
PubMed2006

Strained enamines as versatile intermediates for stereocontrolled construction of nitrogen heterocycles.

This contribution assesses the synthetic utility of molecules that impose conformational constrains onto aziridine-derived enamines. Synthetically versatile [3.1.0] and [4.1.0] bicyclic enamines have been prepared by intramolecular oxidative cycloamination of aziridine-containing olefins. This process is initiated by N-bromosuccinimide followed by base-mediated elimination of HBr to afford highly strained exo-bicyclic enamines. In addition, intramolecular aziridine addition to aldehyde functionality was found to afford the [3.1.0] and [4.1.0] bicyclic hemiaminals. These routes highlight possibilities for chemoselective oxidative transformations of aziridine-containing precursors without nitrogen protection/deprotection steps. The resulting products provide straightforward synthetic entries into a wide range of pyrrolidine- and piperidine-containing heterocycles that are positioned toward subsequent transformations via aziridine ring opening.

Journal Article↗
PubMed2006

Highly regioselective transformation of alkenyl bromides into alpha-bromoaziridines and alpha-bromohydrazones.

[reaction: see text] The synthetic utility of alpha-halohydrazones is an underexplored area due to the lack of chemo- and regioselective routes towards these molecules. Herein, we describe a general method for alpha-bromohydrazone synthesis via the rearrangement of alpha-bromoaziridines, which can be readily prepared for the first time from the corresponding alkenyl bromides. The rearrangement of alpha-bromoaziridines into alpha-bromohydrazones proceeds with high yields and with high selectivities.

Journal Article↗
PubMed2006

Advances in nitrogen transfer reactions involving aziridines.

In recent years, our search for new nitrogen transfer reactions has concentrated on aziridine chemistry. This Account highlights our efforts toward the synthesis and functionalization of aziridines. In the course of our research, we have investigated the electrochemical aziridination of olefins, the acid-catalyzed ring opening of aziridines, and the development of transition metal mediated nitrogen allylation, arylation, and alkenylation of unprotected aziridines. Our studies have also involved the synthesis of aziridine-based enamine intermediates and their stereoselective transformations into heterocyclic compounds.

Journal Article↗
PubMed2006

Making carbon-nitrogen bonds in biological and chemical synthesis.

The function of many biologically active molecules requires the presence of carbon-nitrogen bonds in strategic positions. The biosynthetic pathways leading to such bonds can be bypassed through chemical synthesis to synthesize natural products more efficiently and also to generate the molecular diversity unavailable in nature.

Biological Factors↗
PubMed2005

New insights into the mechanism of palladium-catalyzed allylic amination.

A comparative investigation into palladium-catalyzed allylic amination of unsubstituted aziridines and secondary amines has been carried out. The use of NH aziridines as nucleophiles favors formation of valuable branched products in the case of aliphatic allyl acetates. The regioselectivity of this reaction is opposite to that observed when other amines are used as nucleophiles. Our study provides evidence for the palladium-catalyzed isomerization of the branched (kinetic) product formed with common secondary amines into the thermodynamic (linear) product. In contrast, the branched allyl products obtained from unsubstituted aziridines do not undergo the isomerization process. Crossover experiments indicate that the isomerization of branched allylamines is bimolecular and is catalyzed by Pd(0). The reaction has significant solvent effect, giving the highest branched-to-linear ratios in THF. This finding can be explained by invoking the intermediacy of sigma-complexes, which is consistent with NMR data. The apparent stability of branched allyl aziridines towards palladium-catalyzed isomerization is attributed to a combination of factors that stem from a higher degree of s-character of the aziridine nitrogen compared to other amines. The reaction allows for regio- and enantioselective incorporation of aziridine rings into appropriately functionalized building blocks. The resulting methodology addresses an important issue of forming quaternary carbon centers next to nitrogen. The new insights into the mechanism of palladium-catalyzed allylic amination obtained in this study should facilitate synthesis of complex heterocycles, design of new ligands to control branched-to-linear ratio, as well as absolute stereochemistry of allylamines.

Journal Article↗
PubMed2005

Transition metal-catalyzed synthesis and reactivity of N-alkenyl aziridines.

[reaction: see text] Straightforward methods for palladium-catalyzed alkenylation of aziridines with alkenyl halides and copper-catalyzed alkenylation of aziridines with alkenyl boronic acids have been developed. This methodology offers attractive alternatives to the known methods requiring activated alkenyl halides and acetylenes. A wide variety of N-alkenyl aziridines containing substituents other than electron-withdrawing substituents such as cyano groups and sulfones have been synthesized in good yields. Furthermore, these N-alkenyl aziridines exhibit quite a different reactivity from conventional enamines, as demonstrated by their reactivity.

Journal Article↗
PubMed2005

Development of electrochemical processes for nitrene generation and transfer.

An electrochemical strategy for running nitrogen-transfer reactions on chemically inert anode surfaces has been developed. The generation and trapping of highly reactive nitrene-transfer reagents can be accomplished under mild conditions on platinum electrodes. The key factor that accounts for the high levels of chemoselectivity in this process is the phenomenon of overpotential. We have found that molecules that are similar in terms of propensity toward oxidation can be differentiated on the basis of their affinity to a given electrode surface. Thereby, reactive species can be selectively generated in the presence of acceptor molecules of interest. Specifically, a wide range of structurally dissimilar olefins can be transformed into the corresponding aziridines in the presence of N-aminophthalimide. Likewise, nitrene generation in the presence of sulfoxides leads to their chemoselective transformation into the corresponding sulfoximines. In this paper we discuss the underlying mechanistic foundation of these reactions.

Journal Article↗
PubMed2004

Unusual selectivity of unprotected aziridines in palladium-catalyzed allylic amination enables facile preparation of branched aziridines.

Functionalized branched aziridines can be prepared in high yields and with high levels of regioselectivity using unprotected aziridines as nitrogen sources in palladium-catalyzed allylic amination. High levels of enantioselectivity can be achieved with BINAP on palladium. This methodology allows for strategic placement of an aziridine-containing fragment within a complex molecule environment for further elaboration.

Journal Article↗
PubMed2003

Oxidative cycloamination of olefins with aziridines as a versatile route to saturated nitrogen-containing heterocycles.

Highly reactive [5,3] and [6,3] bicyclic aziridines can be readily prepared from the corresponding NH aziridines and N-bromosuccinimide by intramolecular oxidative cycloamination of olefins. These compounds, including surprisingly stable exo-methylene bicyclic aziridines, provide versatile synthetic entries into a wide range of pyrrolidine- and piperidine-containing heterocycles.

Journal Article↗
PubMed2003

N-arylation of aziridines.

A range of N-arylaziridines were prepared by the palladium or copper catalyzed amination reaction between N-H aziridines and aryl bromides or arylboronic acids. These results showcase the synthetic utility of metal-bound aziridine species in nitrogen transfer processes.

Journal Article↗
PubMed2002

Design and development of cyclohexane-based P,N-ligands for transition metal catalysis.

[reaction: see text] A new class of cyclohexane-based P,N-ligands is readily obtained through aziridine ring opening with suitable phosphorus nucleophiles under acidic conditions. trans-1-Amino-2-diphenylphosphinocyclohexane is resolved with tartaric acid to give the final product in >99% ee. The new ligands show high stability toward oxidation at the phosphorus atom.

Journal Article↗
PubMed2002

Electrochemical imination of sulfoxides using N-aminophthalimide.

[reaction: see text] A novel electrochemical sulfoxide imination process is described. Our approach starts with a highly selective nitrene transfer from N-aminophthalimide to a variety of sulfoxides. This oxidative treatment is followed by reductive N-N bond cleavage under the controlled current conditions, which leads to a range of parent NH sulfoximines. In addition to solving the challenging problem of removing the N-phthalimido group, the overall process avoids the use of toxic oxidants and metal additives.

Electrochemistry↗