Synthesis of polysubstituted 3-hydroxypyridines via the revisited hetero-Diels–Alder reaction of 5-alkoxyoxazoles with dienophiles

De Novo Synthesis of Polysubstituted 3-Hydroxypyridines Via “Anti-Wacker”-Type Cyclization

We report an efficient method to prepare polysubstituted 3-hydroxypyridines from amino acids, propargyl alcohols, and arylboronic acids. The process involves Pd(0)-catalyzed anti-selective arylative cyclizations of N-propargyl-N-tosyl-aminoaldehydes with arylboronic acids (“anti-Wacker”-type cyclization), oxidation of the resulting 5-substituted-3-hydroxy-1,2,3,6-tetrahydropyridines to 3-oxo derivatives, and elimination of p-toluenesulfinic acid. This method provides diverse polysubstituted 3-hydroxypyridines, whose hydroxy group can be further substituted by a cross-coupling reaction via a triflate.

Dearomatization of a 3-Hydroxypyridine Through an Unexpected Oxidative Deformylation Process: An Entry to Azacyclohexadienones

Phenols are well-known precursors of cyclohexadienones, which have widespread applications in organic synthesis. In contrast, their hydroxypyridine counterparts have not been explored yet. An unprecedented oxidative dearomatization of a 3-hydroxypyridine involving an unexpected deformylation step is reported. The chemical reactivity of the resulting unreported azacyclohexadiene-type compound was also explored.

Maleimide-based metal-free ligation with dienes: a comparative study

Maleimide-based Diels–Alder strategies for bioconjugation are compared in terms of dienes accessibility and stability, reactions rates, as well as products isolation and stability.

Isolation of a 3-hydroxypyridine degrading bacterium, Agrobacterium sp. DW-1, and its proposed degradation pathway

A 3-hydroxypyridine degrading bacterium, designated strain DW-1, was isolated from petroleum contaminated soil in Liao River China. 16S rRNA-based phylogenetic analysis indicates that strain DW-1 belongs to genus Agrobacterium. The optimal cultivation temperature and pH for strain DW-1 with 3-hydroxypyridine were 30 °C and 8.0, respectively. Under optimal conditions, strain DW-1 could completely degrade up to 1500 mg/L of 3-hydroxypyridine in 66 h. The 3-hydroxypyridine degradation pathway of strain DW-1 was suggested by HPLC and LC-MS analysis. The first reaction of 3-hydroxypyridine degradation in strain DW-1 was α-hydroxylation so that the major metabolite 2,5-dihydroxypyridine was produced, and then 2,5-dihydroxypyridine was transformed by a Fe2+-dependent dioxygenase to form N-formylmaleamic acid. N-Formylmaleamic acid will be transformed to maleic acid and fumaric acid through maleamic acid. This is the first report of the 3-hydroxypyridine degradation pathway and the utilization of 3-hydroxypyridine by a Agrobacterium sp. It may be potentially used for the bioremediation of environments polluted with 3-hydroxypyridine.

Metal triflate promoted synthesis of naphthalenes

A synthetic route to derive the skeleton of naphthalenes starting with isovanillin is described with modest total yields via the key transformation of metal triflate-mediated intramolecular benzannulation of o-formyl or o-benzoyl allylbenzenes in MeNO₂ at rt.

Synthesis of annulated pyridines as inhibitors of aldosterone synthase (CYP11B2)

A series of potent and selective aldosterone synthase (CYP11B2) inhibitors were prepared in one step through an intermolecular Kondrat'eva reaction.

Three steps in one pot: synthesis of linear bilateral extended 2,2':6',2″-terpyridineruthenium(II) complexes

Metal complexes of linear bilateral extended 2,2':6',2″-terpyridine [2,6-bis(2-substituted furo[2,3-c]pyridin-5-yl)pyridine] are topological tridentate analogues of 5,5'-functionalized 2,2'-bipyridine. The present methodology provides access to linear bilateral extended 2,2':6',2″-terpyridineruthenium(II) complexes starting from 5,5″-bis(methoxymethoxy)-4,4″-bis(substituted ethynyl)-2,2':6',2″-terpyridines via one-pot cleavage of the methoxymethyl (MOM) protecting group, cycloisomerization, and metal complexation in the presence of Ru(DMSO)4Cl2. In this reaction, ruthenium(II) likely plays a triple role, acting as a Lewis acid to cleave the MOM ether, a catalyst facilitating 5-endo-dig cyclization, and a coordination metal center, being an integral part of the final product.

The first "ready-to-use" benzene-based heterotrifunctional cross-linker for multiple bioconjugation

The synthesis and applications of the first water-soluble benzene derivative bearing a set of three different and orthogonal bioconjugatable groups (aminooxy, azido and thiol) are described. The combined use of a 5-amino isophthalic acid scaffold and unusual acid-labile protecting groups for temporarily masking aminooxy and thiol moieties has enabled the development of a highly convergent approach towards the synthesis of such a trivalent bioconjugation platform in good yields. The potential utility of this "ready-to-use" cross-linking reagent for creating complex and fragile tri-component (bio)molecular systems was illustrated through (1) the rapid preparation of a three-colour FRET cascade with valuable spectral properties and (2) the luminescent/fluorescent labelling of peptides and peptide-oligonucleotide conjugates. Thus, such (bio)molecular assemblies were readily obtained via a three-step process or in a "one-pot" manner, both involving oxime ligation, thiol-alkylation (S(N)2 or Michael addition) and copper-catalysed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) reactions.

The Kondrat'eva reaction in flow: direct access to annulated pyridines

A continuous flow inverse-electron-demand Kondrat'eva reaction has been developed that provides direct access to cycloalka[c]pyridines from unactivated oxazoles and cycloalkenes. Annulated pyridines obtained by this one-step process are valuable scaffolds for medicinal chemistry.

Efficient synthesis of oxazoles by dirhodium(II)-catalyzed reactions of styryl diazoacetate with oximes

An efficient one-step synthesis of multi-functionalized oxazole derivatives is achieved in high yield by dirhodium(II)-catalyzed reactions of styryl diazoacetate with aryl oximes.

Highly regio- and stereoselective Diels-Alder cycloadditions via two-step and multicomponent reactions promoted by infrared irradiation under solvent-free conditions

Infrared irradiation promoted the Diels-Alder cycloadditions of exo-2-oxazolidinone dienes 1-3 with the Knoevenagel adducts 4-6, as dienophiles, leading to the synthesis of new 3,5-diphenyltetrahydrobenzo[d]oxazol-2-one derivatives (7, 9, 11 and 13-17), under solvent-free conditions. These cycloadditions were performed with good regio- and stereoselectivity, favoring the para-endo cycloadducts. We also evaluated the one-pot three-component reaction of active methylene compounds 20, benzaldehydes 21 and exo-2-oxazolidinone diene 2 under the same reaction conditions. A cascade Knoevenagel condensation/Diels-Alder cycloaddition reaction was observed, resulting in the final adducts 13-16 in similar yields. These procedures are environmentally benign, because no solvent and no catalyst were employed in these processes. The regioselectivity of these reactions was rationalized by Frontier Molecular Orbital (FMO) calculations.