Acyl nitroxides. Part I. Synthesis and isolation

Alewood, Paul F.; Hussain, Syeed; Jenkins, Terence C.; Perkins, M. J.; Sharma, Ashutosh H.; Siew, Nancy P. Y.; Ward, Peter A.

doi:10.1039/p19780001066

Cited by 37 publications

(23 citation statements)

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“…Should this be the case, then-assuming an analogous reaction course-the thiocarbonyl complex (3) ought to be formed from CSSe and (1) via the intermediate (6). This expectation is only partially fulfilled.…”

Section: Thiocarbonyl-metal Complexes From Csse"'mentioning

confidence: 90%

“…After removal of ether, (1) and (7) were separated by bulb-to-bulb distillation; example: ( 7 4 , b. p. 50-55 "C/ 0. 6 The asymmetric inductions in the case of the diethyl lactim ether are as high as in the case of (3). but the 'H-NMR spectra are less clear.…”

Section: Methodsmentioning

confidence: 96%

“…This expectation is only partially fulfilled. On reaction of (1) with thiocarbonyl selenide at -20 "C in toluene a mixture of (3) and (6) is obtained, which owing to the difference in solubility of the complexes in hexane [ (3) is readily soluble and (6) is only sparingly soluble] can be easily separated. (6) reacts with PPh, in benzene (50 "C, 1 h) to give (3) in quantitative yield.…”

Section: Thiocarbonyl-metal Complexes From Csse"'mentioning

confidence: 99%

“…Table l ) were determined on the crude product. The compounds (6) were purified by bulb-to-bulb distillation; example: (6a), b. p. 115-120 "C/0.6 torr; IR (film): w=1680 cm-' (N-C); 'H-NMR (CDCI,): 6=3.62 and 3.60 (each s, OCH,), 1.44 (s, 6-CH3), 1.16 and 0.40 (each d, J = 7 Hz, 3-CH3 for trans-(6a) and cis-(6a)['', intensity ratio z 28 : l), 3.17 (q, J = 7 Hz, 3-H), 3.11 and 2.74 (AB, J = 14 Hz, CHI).Hydrolysis of (6) to (7): A suspension of (6) (10 mmol) in 0.5 N hydrochloric acid was stirred for 20 min-2 h at room temperature. The solvent was removed in a vacuum (50 "C), the residue [(7).HCI] taken up in a ca.…”

mentioning

confidence: 99%

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Enantioselective Oxidation by a Chiral Acylaminyl Oxide

Berti¹,

Perkins²

1979

Angew. Chem. Int. Ed. Engl.

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of the alkylation can be determined, either 'H-NMR spectroscopically at the stage of the alkylation product (6) or polarimetrically or NMR spectroscopically with chiral shift reagents at the stage of the a-methyl-a-aminocarboxylate (7) or a-methyl-a-amino acid.We obtained 3,6-dihydropyrazine (3) by reaction of cyclo-(L-Ala-L-Ala) (2)I2I with trimethyloxonium tetrafluoroborate. This reaction proceeds without racemization. The lithiation of (3) to (4) can be smoothly performed at -70 "C (in tetrahydrofuran) with butyllithium or lithium diisopropylamide (LDA). Double metalation at C-3, which would lead to an antiaromatic 8 T electron system, does not take place[31. The alkylation products (6) are hydrolyzable with 0.5 N hydrochloric acid even at room temperature. The esters ( I ) and (7) can be separated, for instance, by distillation.In the alkylation (4) + (6), the R-configuration is induced at C-6, i. e. the alkyl moiety prefers the trans-position to the methyl group at C-3. For example, (R)-( -)-a-methylphenylalanine['"I is obtained from (6a) via the ester (7a). In (6a) the R-configuration at C-6 is recognizable in the 'H-NMR spectrum: 3-H absorbs at relatively high field strengths (6=3.17) because it is situated in the shielding anisotropic region of the phenyl group, which probably lies in a .rr-complex fashion over the hetero~ycle[~l. We attribute the high asymmetric induction to the fact that one of the two diastereotopic sides of the probably planar anion of (4) is relatively strongly shielded by the methyl group. Experimental(2): After washing with ether, the crude product obtained according to is ca. 90% optically pure. Crystallization twice from water yielded almost optically pure (2); [ a J g = 26.4" (c=1.3, H20); after drying in a vacuum over P205, m.p. 289 "C.(3): A mixture of (2) (14.2 g, 0.1 mol) in anhydrous CH2C12 (300 ml) and trimethyloxonium tetrafluoroborate was vigorously stirred or shaken for 34 h at room temperature15]. A buffer solution, consisting of NaH2P04 (40.0 g, 0.3 mol) and Na2HP04 (113.7 g, 0.8 mol) in 500 ml water, was added to the ice-cold mixture, the organic phase was separated off and the aqueous phase extracted three times with CH2C12. The combined extracts were dried over MgSO, and then evaporated to dryness at 10 torr; yield 14.9 g (88%) of almost optically pure (3), b.p. Alkylation of (3) to (6): A solution of butyllithium (10 mmol, 6.4 ml of a 1.55 N solution in hexane) (or 10 mmol lithium diisopropylamide in a little THF) is cooled to -70 "C and then added dropwise to a solution of (3) (1.7 g, 10 mmol) in anhydrous T H F (20 ml) at -70 "C. The mixture is stirred for 10 min at this temperature, treated with a solution of (5) (10 mmol) in THF (10 mmol) and stirring continued for 2-10 h. The mixture is allowed to warm to room temperature, the solvent removed at 10 torr, the residue treated with 10 ml water (and if necessary 5 g common salt), extracted three times with 30 ml of ether or CH2C12, the extracts combined, dried over MgSO, and worked-up in the usual way. Diastereo...

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Section: Thiocarbonyl-metal Complexes From Csse"'mentioning

confidence: 90%

Section: Methodsmentioning

confidence: 96%

Section: Thiocarbonyl-metal Complexes From Csse"'mentioning

confidence: 99%

mentioning

confidence: 99%

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Enantioselective Oxidation by a Chiral Acylaminyl Oxide

Berti¹,

Perkins²

1979

Angew. Chem. Int. Ed. Engl.

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“…[19] Methode b geht von Hydroxylaminen aus: Diese werden erfolgreich mit milderen Oxidationsmitteln [19] wie Nickelperoxid, [20] Kaliumferricyanid, [20] Blei(IV)-oxid, [21] Silberoxid, [22] Mangan(IV)-oxid [23] und besonders häufig Natriumperiodat [24] zu den entsprechenden Nitroxiden umgesetzt. Zum Teil kann unter basischen Bedingungen auch molekularer Sauerstoff ohne jegliches Additiv als Oxidationsmittel zum Einsatz kommen.…”

Section: Synthese Von Nitroxidenunclassified

Nitroxide: Anwendungen in der Synthese und in der Polymerchemie

2011

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Nitroxide werden in der Synthese und in der Polymerchemie verwendet. In diesem Aufsatz werden zunächst Methoden zur Herstellung von Nitroxiden und deren physikalische Eigenschaften besprochen. Der folgende Abschnitt beschreibt die Verwendung von Nitroxiden als stöchiometrische und katalytische Oxidationsmittel in der organischen Synthese. Die Oxidation von Alkoholen und Carbanionen spielt dabei ebenso eine wichtige Rolle wie oxidative C‐C‐Bindungsknüpfungen. Anschließend widmet sich ein Abschnitt der Rolle von Nitroxiden als Abfangreagentien für C‐zentrierte Radikale in der Radikalchemie. Nitroxide, die sich von Alkoxyaminen ableiten, fungieren als nützliche Ausgangsmaterialien für C‐zentrierte Radikale, deren Einsatz in der Synthese und in der Polymerchemie beschrieben wird. Der letzte Abschnitt stellt die Grundlagen der Nitroxid‐vermittelten Polymerisation (NMP) vor und zeigt neuere Entwicklungen beim Design komplexer Polymerarchitekturen auf.

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