Dehydrierung von Ketonen mit Palladium(II)‐Verbindungen

Bierling, Bernd; Kirschke, Klaus; Oberender, H.; Schulz, Manfred

doi:10.1002/prac.19723140121

Cited by 46 publications

(5 citation statements)

References 6 publications

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“…These dehydrobrominations usually require quite vigorous conditions.1 This note reports our attempts to develop a mild method for this type of elimination using palladium tetrakis(triphenylphosphine) , 2 It was hoped that Pd(PPh3)4 would undergo facile oxidative addition with «-bromo ketones just as Pd(0) complexes do with other organic halides.3 The resulting species, for which one possible representation is shown in eq l,4•5 might be expected to expel a ß hydrogen along with palladium to form enone.® Presumably, the intermediate(s) involved would be similar to those in the direct oxidation of ketones to enones using Pd(II) salts. [7][8][9] The proposed method offers the potential advantage of regioselectivity in enone formation and could, in principle, be catalytic in palladium without added Cu(II) salts. 7•9 The method works well in the case of 2-bromo-l-tetralones, where the initially formed enone can aromatize simply by tautomerization.…”

Section: References and Notesmentioning

confidence: 99%

Dehydrobromination of .alpha.-bromo ketones with palladium tetrakis(triphenylphosphine)

Townsend¹,

Reingold²,

Kendall³

et al. 1975

J. Org. Chem.

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Section: References and Notesmentioning

confidence: 99%

Dehydrobromination of .alpha.-bromo ketones with palladium tetrakis(triphenylphosphine)

Townsend¹,

Reingold²,

Kendall³

et al. 1975

J. Org. Chem.

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“…Efforts were then focused toward the key aromatization step. Initial attempts to oxidize the silyl dienol ether of 7 and 8 with palladium 10 or MnO 2 11 saw competitive oxidation of the indenotetrahydropyridine core. Several other attempts to oxidize the dienolate or cyclohexenone directly also failed.…”

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confidence: 99%

Scalable Total Synthesis and Biological Evaluation of Haouamine A and Its Atropisomer

et al. 2009

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Haouamine A 1 (1, Figure 1) is a biologically active and architecturally unique alkaloid whose striking feature is a [7]-azaparacyclophane macrocycle containing a highly deformed nonplanar aromatic ring. Somewhat mysteriously, 1 was discovered to exist as a mixture of two rapidly interconverting isomers in solution, a quality attributed to either atropisomerism of the bent arene or slowed pyramidal inversion at nitrogen. Recent computational work 2 supported a theory coupling the latter process with conformational reorganization of the tetrahydropyridine ring but could not rule out atropisomerism. 3 The total synthesis of 1 from this laboratory 4 also did not answer this question unequivocally due to an inability to control the atropisomer formed in the low-yielding cyclophaneforming step, which fortuitously favored the natural planar stereochemistry. 5,6 Here, we report a scalable and controllable route to 1 and its atropisomer (2) that features point-to-planar chirality transfer 7 via a one-step, chemoselective cyclohexenone to phenol oxidation to introduce strain within the macrocycle, a reaction that may find future use in strained chiral cyclophane synthesis. We also demonstrate that the strained cyclophane in 1 is crucial for anticancer activity in PC3 cells.To program planar chirality within the cyclophane macrocycle a reduced compound (3, Figure 1) was selected as the bent phenol precursor. Molecular models suggested that hybridization change of one of the para carbons of the cyclophane from sp 2 to sp 3 should significantly reduce the strain present within the macrocycle and thus make for an accessible intermediate 5c (numerous attempts to form the macrocycle with a preinstalled phenol in this 4 and other 5,6 laboratories have all failed). Furthermore, it was surmised that the point chirality introduced by such a change in hybridization could be used to select for the planar chirality present in 1 and 2. Saturated cyclophane 3 could then be traced † The Scripps Research Institute. ‡ Genentech Inc. 3 equiv), -78°C (for 7) or -95°C (for 8), 1 min, 60% of 9 + 23% 7, or 61% of 10; (e) BBr 3 (7.0 equiv), CH 2 Cl 2 , -78 to 5°C, 20 h, 63% for 1, or 60% for 2.

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“…The key intermediate 3 was obtained from commercially available citronellal 2 following a reported procedure. 3 The ketone 3 was exposed 4 to PdCl 2 in t-butanol containing 4 equivalent of Na 2 CO 3 at 80 °C to afford (-)-1 in 68%.…”

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confidence: 99%

The first synthesis of (–)-4-(1,5-dimethylhex-4-enyl)-2-methylphenol

Shan

2004

Journal of Chemical Research

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Dehydrierung von Ketonen mit Palladium(II)‐Verbindungen

Abstract: Cyclohexanon reagiert mit Palladium(II)‐Verbindungen in einer stöchiometrischen Reaktion unter Dehydrierung zum Cyclohexen‐(2)‐on. Diese Dehydrierungsreaktion ist allgemein auf Ketone anwendbar. Der Mechanismus der Reaktion wird diskutiert.

Cited by 46 publications

References 6 publications

Dehydrobromination of .alpha.-bromo ketones with palladium tetrakis(triphenylphosphine)

Dehydrobromination of .alpha.-bromo ketones with palladium tetrakis(triphenylphosphine)

Scalable Total Synthesis and Biological Evaluation of Haouamine A and Its Atropisomer

The first synthesis of (–)-4-(1,5-dimethylhex-4-enyl)-2-methylphenol

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