An allylpalladium(IV) intermediate in the synthesis of highly substituted benzoxepines and benzopyrans via reactions of stable pallada(II)cycles with allyl bromides

Organometallics

Volumn 26, Issue 15, 2007, Pages 3874-3883

  Guo, Ruiyun ^a   Portscheller, Janelle L ^a   Day, Victor W ^a   Malinakova, Helena C ^a  

^a UNIVERSITY OF KANSAS   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ALLYL BROMIDES; BENZOPYRANS; BENZOXEPINES; BIPYRIDINE;

LIGANDS; ORGANOMETALLICS; REACTION KINETICS; SUBSTITUTION REACTIONS; SYNTHESIS (CHEMICAL); X RAY CRYSTALLOGRAPHY;

PALLADIUM COMPOUNDS;

EID: 34547473085     PISSN: 02767333     EISSN: None     Source Type: Journal    
DOI: 10.1021/om7002865     Document Type: Article

References (40)

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30. 13C NMR spectroscopy.
31. 13C NMR spectroscopy. Its formation can be rationalized via C-allylation of the palladium ester enolate VII (Figure 2) with the allyl bromide.
32. 13C NMR spectroscopy. Its formation can be rationalized by -hydride elimination following migratory insertion from intermediate X (Figure 2) occurring with the regiochemistry, giving rise to a benzopyran with an exocyclic double bond, which isomerizes to the more stable structure shown below.
33. 1H NMR NOE experiments performed on benzopyrans 5a,b detected the following correlations: (i) the methine proton bonded to carbon C2 showed an NOE correlation to a proton on the vinylic carbon directly bonded to C3 (for 5a) or to a terminal proton in the vinyl side chain bonded to carbon C3 (for 5b). However, inspection of the molecular models of different conformations of benzopyrans 5a,b revealed that these correlations could be present in both cis and trans heterocycles.
34. Examples of palladation of aromatic rings directed by a heteroatom-containing substituent in the Ortho position are well-known; see: Dupont, J.; Consorti, C. S.; Spencer, J.Chem. Rev. 2005, 105, 2527.
35. 13C NMR spectroscopy. Heterocycle 13b may arise via Pd-mediated decarboxylation following the formation of a benzoxepine substituted with the Pd atom at C-3 via readdition of the H-Pd-X complex to the double bond formed via β-hydride elimination. The heterocycle 13c could arise via air oxidation of 13b.
36. 1H NMR). Under optimum conditions (8.5 h, 0 °C) the molar ratio 12:3b:11 was 10:2:1.
37. c) and a single carbon at 38.1 ppm.
38. 3) single-domain crystals obtained for the two different solvent polymorphs gave acceptable yields of data to 2θ(Mo Kα) = 45.0°. Even though the lower yield of data for both polymorphs necessarily reduces the precision of the resulting structural parameters, all three molecules have the same Pd stereochemistry and consistent Pd-ligand bond lengths.
39. 3) = 2.043 Å, Pd-N(1,2) = 2.114, 2.126 Å.
40. The half-life is approximately 3 h.