Synthesis of 2,4,6-Trisubstituted Chiral Piperidines and (−)-Dendroprimine by One-Pot Asymmetric Azaelectrocyclization Protocol

The 6π-azaelectrocyclization of azatrienes. Synthetic applications in natural products, bioactive heterocycles, and related fields

Covering: 2006 to 2018 The application of the 6π-azaelectrocyclization of azatrienes as a key strategy for the synthesis of natural products, their analogs and related bioactive or biomedically-relevant compounds (from 2006 to date) is comprehensively reviewed. Details about reaction optimization studies, relevant reaction mechanisms and conditions are also discussed.

Redox cycloisomerization approach to 1,2-dihydropyridines

The phosphine-catalyzed synthesis of 1,2-dihydropyridines via an alkyne isomerization/electrocyclization sequence is described. Propargylidenecarbamate substrates were prepared following a one-pot procedure between a terminal alkyne, a benzonitrile, and a chloroformate in the presence of trimethylaluminum. This methodology gives access to a diverse set of 2,6-disubstituted 1,2-dihydropyridines in high yield. The products can be easily converted into substituted piperidines or pyridines, and this methodology was applied to the synthesis of indolizidines.

Cellulose sulfonic acid as a green, efficient, and reusable catalyst for Nazarov cyclization of unactivated dienones and pyrazoline synthesis

A high yielding and eco-friendly procedure for the preparation of cyclopentenoid and pyrazoline derivatives via cellulose sulfonic acid-mediated electrocyclization processes.

Access to optically active 3-substituted piperidines by ring expansion of prolinols and derivatives

The ring expansion of prolinols via an aziridinium intermediate gives C3-substituted piperidines in good yields and enantiomeric excess, the substituent at the C3 position being derived from the most reactive nucleophile in the reaction mixture. Depending on the nucleophile, the reaction proceeds under thermodynamic or kinetic control. The regioselectivity of attack of nucleophiles on the aziridinium intermediate depends on the nature of the substituents on the nitrogen atom and the C4 position of the starting prolinols.

Chemical Approach to a Whole Body Imaging of Sialo-N-Linked Glycans

PET and noninvasive fluorescence imaging of the sialo-N-linked glycan derivatives are described. To establish the efficient labeling protocol for N-glycans and/or glycoconjugates, new labeling probes of fluorescence and ⁶⁸Ga-DOTA, as the positron emission nucleus for PET, through rapid 6π-azaelectrocyclization were designed and synthesized, (E)-ester aldehydes. The high reactivity of these probes enabled the labeling of lysine residues in peptides, proteins, and even amino groups on the cell surfaces at very low concentrations of the target molecules (~10⁻⁸ M) within a short reaction time (~5 min) to result in "selective" and "non-destructive" labeling of the more accessible amines. The first MicroPET of glycoproteins, ⁶⁸Ga-DOTA-orosomucoid and asialoorosomucoid, successfully visualized the differences in the circulatory residence of glycoproteins, in the presence or absence of sialic acids. In vivo dynamics of the new N-glycoclusters, prepared by the "self-activating" Huisgen cycloaddition reaction, could also be affected significantly by their partial structures at the non-reducing end, i.e., the presence or absence of sialic acids, and/or sialoside linkages to galactose. Azaelectrocyclization chemistry is also applicable to the engineering of the proteins and/or the cell surfaces by the oligosaccharides; lymphocytes chemically engineered by sialo-N-glycan successfully target the tumor implanted in BALB/C nude mice, detected by noninvasive fluorescence imaging.

Enantiodivergency and enantioconvergency in the synthesis of the dendrobate alkaloid 241D

A diastereodivergent preparation of two N-alkenylnitrones (9 and 11) from easily available (R)-2,3-O-cyclohexylideneglyceraldehyde (5) led to an enantiodivergent synthesis of both enantiomers of the dendrobate alkaloid 241D in a sequential two-directional approach involving intramolecular nitrone cycloaddition as the key step. Either of these two nitrones could, in principle, be utilized for the preparation of the title compounds in an enantioconvergent fashion as well. The methodology was extended to prepare an analogue (33) of (-)-241D.

Cell surface biotinylation by azaelectrocyclization: easy-handling and versatile approach for living cell labeling

Versatile method for living cell labeling has been established. Cell surfaces are initially biotinylated by azaelectrocyclization, and then treated with the fluorescence-labeled avidin or the anti-biotin antibody.

Synthesis of enantiopure substituted piperidines via an aziridinium ring expansion

Herein we report a novel methodology for the asymmetric synthesis of 3-substituted piperidines from readily available chiral building blocks. This method, which features a novel irreversible dihydropyrole-tetrahydropyridine ring expansion, allows the introduction of a large variety of substituents at the 3-position and permits substitution at the 2- and 6-position giving mono-, di-, or trisubstituted piperidines with high diastereocontrol.

Target-selective fluorescent "switch-on" protein labeling by 6π-azaelectrocyclization

Application of azaelectrocyclization and FRET techniques to lysine groups enabled the selective and sensitive detection of a target protein from a mixture, with high fluorescence contrast.

Asymmetric electrocyclic reactions

This critical review offers an overview of asymmetric electrocyclic processes, where diastereo- or enantioselectivity is a consequence of the influence of a chiral component (be it substrate or catalyst) on the electrocyclic bond-forming process (195 references).

Library-directed solution- and solid-phase synthesis of 2,4-disubstituted pyridines: one-pot approach through 6pi-azaelectrocyclization

An efficient one-pot synthetic procedure for the synthesis of 2,4-disubstituted pyridines has been successfully established. The method proceeds through a 6pi-azaelectrocyclization-aromatization sequence. Using this method, a wide variety of pyridine structures substituted at the 2-position have been rapidly constructed from vinyl stannanes, vinyl iodide, sulfonamide, and a palladium catalyst. The method was further applied to the solid-phase synthesis wherein the use of a "traceless" sulfonamide linker enabled the rapid preparation of a small library of pyridines with high purity, without any chromatographic separation.

A convenient allylsilane-N-acyliminium route toward indolizidine and quinolizidine alkaloids

This review relates all the results that we obtained in the field of the total synthesis of indolizidine and quinolizidine alkaloids using a strategy of the addition of an allylsilane on an N-acyliminium ion. In this paper, we describe the synthesis of racemic indolizidine 167B and chiral indolizidines: (-)-indolizidines 167B, 195B, 223AB, (+)-monomorine, (-)-(3R,5S,8aS)-3-butyl-5-propylindolizidine and (-)-dendroprimine. Next, we relate the synthesis that we have developed in the quinolizidines field: (±)-myrtine and epimyrtine, (±)-lasubines I and II and chiral quinolizidines: (+)-myrtine, (-)-epimyrtine, (-)-lasubines I and II and (+)-subcosine II.

Asymmetric synthesis of ring functionalized trans-2,6-disubstituted piperidines from N-sulfinyl delta-amino beta-keto phosphonates. total synthesis of (-)-myrtine

Sulfinimine-derived N-sulfinyl delta-amino beta-ketophosphonates are transformed via the enaminones to the phosphoryl dihydropyridones that selectively give trans-2,6-disubstituted 1,2,5,6-tetrahydropyridines on organocuprate addition and dephosphorylation.