The photochemical and thermal reactions of a triosmium cluster carrying a γ-pyrone ligand with alkynes

The reaction of the cluster Os₃(CO)₁₀(μ-H)(μ-γ-C₅H₃O₂) (1) with a number of alkynes under thermal or visible light irradiation conditions, afforded in most cases the dinuclear complexes Os₂(CO)₆(μ-γ-C₅H₃O₂)(μ-LH) (L=PhCCPh, ^tBuCCH, ^tBuCCMe or EtCCEt) (2) or the trinuclear chain complexes Os₃(CO)₉(μ-H)(μ-γ-C₅H₃O₂)(μ-RCCHC₆H₄) (R=H, Ph) (3). In the case of PhCCPh, a new isomer of Os₃(CO)₈(PhCCPh)₂, viz., Os₃(CO)₈(μ-PhCCPh)(μ-PhCCHC₆H₄) (7) has been isolated and characterised.     

Vilsmeier-Haack reactions of carbonyl compounds: synthesis of substituted pyrones and pyridines

Vilsmeier-Haack reaction of substituted phenylacetones leads to the formation of conjugated iminium salts which on aqueous basic work up afford 3-formyl-4-pyrones and on ammonium acetate-induced cyclization afford 5-aryl-4-chloronicotinaldehydes in good yields.     

Condensation of 2‐Pyrone with 3‐Aminopyrazolone. A Novel Synthesis of Pyrazolo[3,4‐b]pyridines

Abstract

A simple route to the preparation of new heterocyclic systems: pyrazolo[3,4‐b]pyridines from the easily available 2‐pyrone and 3‐aminopyrazolone. The structure of the compounds and the mechanism of their formation are reported.     

Synthesis of polynuclear aromatic compounds through net [5+5]-cycloaddition of 2-alkynylarylcarbene complexes and enyne-aldehyde derivatives

Coupling of o-alkynylphenylcarbene complexes and -o-alkynylheteroarene carboxaldehydes leads to heterocycle annulated phenanthrene derivatives.     

Petrorhagiosides A – D,New γ‐Pyrone Derivatives from Petrorhagia saxifraga Link

Four novel γ‐pyrone (=4H‐pyran‐4‐one) metabolites, petrorhagiosides A–D, along with four known analogs, have been isolated from the MeOH extract of Petrorhagia saxifraga, a perennial herbaceous plant typical of Mediterranean vegetation. The structures of the new compounds were established on the basis of extensive spectroscopic analyses including 1D‐ an 2D‐NMR (¹H,¹H‐DQ‐COSY, TOCSY, HSQC, CIGAR‐HMBC, and HSQC‐TOCSY) experiments.     

Synthesis of isomerically pure 3-(5-trifluoromethyl-1,2,3-triazol-4-yl)cinnamic acid derivatives via the reaction of 4-aryl-6-trifluoromethyl-2-pyrones with sodium azide

Treatment of 4-aryl-6-trifluoromethyl-2-pyrones with sodium azide in DMSO afforded the corresponding (Z)-3-(5-trifluoromethyl-1,2,3-triazol-4-yl)cinnamic acids in good yields. Similarly, 4-aryl-3-carbethoxy-6-trifluoromethyl-2-pyrones smoothly reacted with sodium azide in acetonitrile to produce (E)-2-ethoxycarbonyl-3-(5-trifluoromethyl-1,2,3-triazol-4-yl)cinnamic acids in high yields, whereas their reactions in ethanol, accompanied by a configurational change, gave the thermodynamically more stable (Z)-2-ethoxycarbonyl-3-(5-trifluoromethyl-1,2,3-triazol-4-yl)cinnamic acids.     

Dihydrofurocoumarin and dihydrofurodihydropyrid-2-one derivatives via palladium catalysed cascades involving aryl/heteroaryl/vinyl iodides and allene followed by acid catalysed cyclisation

Mono 3-(2′-arylallyl) derivatives of 4-hydroxycoumarin 1a,b, 4-hydroxy-6-methyl-pyran-2-one (3) and 6-hydroxy-1,4-dimethyl-1,2-dihydropyrid-2-one-3-carbonitrile (4) are produced in 3-component cascades involving aryl/heteroaryl/vinyl iodides and allene (1 atm) using Pd(PPh₃)₄/Cs₂CO₃/MeCN/80 °C or Pd₂(dba)₃/tris(2-furyl)phosphine/K₂CO₃/DMF/80 °C as the catalyst system. 4-Hydroxy-2-quinolone (2) afforded a mixture of mono- and bis-allylation products under these conditions. Mono C-allylation products 5a-e and 15a-e undergo facile acid catalysed cyclisation to afford dihydrofurocoumarins 11a-e and dihydrofurodihydropyrid-2-ones 16a-e in good overall yield.     

Structure of onchidione, a bis-γ-pyrone polypropionate from a marine pulmonate mollusk

The chemical investigation of the marine pulmonate Onchidium sp. and of its defensive mucous secretion led us to the isolation of a novel polypropionate, onchidione (4), containing two γ-pyrone rings. The structure of 4 was elucidated by spectroscopic methods, mainly NMR techniques, and secured by X-ray analysis on a single crystal.     

The photochemical reaction of Os3(CO)10(μ-H)(μ-γ-C5H3O2), a triosmium cluster carrying a γ-pyrone ligand, with dimethylacetylenedicarboxylate: formation of isomeric clusters

The reaction of the cluster Os₃(CO)₁₀(μ-H)(μ-γ-C₅H₃O₂) (1), with DMAD under UV irradiation afforded three isomers of the monosubstituted product, Os₃(CO)₉(μ-γ-C₅H₃O₂)(μ₃-MeO₂CCHCCO₂Me) (2), and a disubstituted product, Os₃(CO)₈(μ-γ-C₅H₃O₂)(μ₃-MeO₂CCHCCO₂Me)(μ-MeO₂CCCCO₂Me) (3). The formation of 3 suggests that flipping of the O-heterocycle can occur.     

Synthesis of pyrone-annulated 2-oxabicyclo[3.3.1]nonanes by palladium-catalyzed cyclization of 4-hydroxy-2-pyrones with allylic bisacetates

Cyclization of 4-hydroxy-2-pyrones with allylic bisacetates by a palladium catalyst is described. Pyrone-annulated 2-oxabicyclo[3.3.1]nonane derivatives were regioselectively produced from the reaction of 4-hydroxy-2-pyrones with 1,4-diacetoxy-2-cyclohexene at high temperature. The reaction would proceed via a migration of the π-allylpalladium intermediate.