Carbonyl carbon chemical shifts in the 13c spectra of cyclic ketones

Langford, Gordon E.; Auksi, Hillar; Gosbee, J. A.; MacLachlan, F. N.; Yates, Peter

doi:10.1016/s0040-4020(01)92038-1

Cited by 21 publications

(6 citation statements)

References 47 publications

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“…It was thus evident that a triplet at ~ 40 ppm (C-6 or C-14) in the spectrum of strychnobrasiline had disappeared and had been replaced by the doublet at 73.0 ppm, which would suggest that the hydroxy group was carried either on C-6 or C-14. That the hydroxy group was borne on C-14 was supported by the fact that the C-ring carbons showed considerable shifts, i.e., C-3 was shifted upheld 3.5 ppm as had also been reported for other hydroxy cyclic ketones (16)(17)(18), whereas the shift for C-5 adjacent to C-6 was relatively small. In addition, an examination of the fragmentation pattern, as proposed by Iwataki and Comin (11), revealed that the fragments containing the C-6 carbon (m/z 130, 143, 144, 185, 186) were still evident in the hydroxy derivative, whereas those (mle 136, 166, 180, 194) bearing the C-14 portion were less abundant than in strychnobrasiline.…”

supporting

confidence: 64%

Alkaloids of Strychnos soubrensis

Ohiri¹,

Verpoorte²,

Svendsen³

et al. 1983

J. Nat. Prod.

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A phytochemical investigation of the chloroform extract of the stern bark of Strychnos soubrenszs Hutch. et Dalz. (Loganiaceae) resulted in the isolation of four alkaloids. Three of them were identified as strychnobrasiline, strychnofendlerine, and isosplendine. The fourth one is a new alkaloid for which we propose the structure 14-P-hydroxy-srrychnobrasiline.The African species of Strychnos has been the object of systematic research in recent years. However, whereas some species have been extensively investigated, others have received little or no attention. Therefore, so far, the knowledge of the African Strychnos species is not complete. In an effort to supply some of the missing information, we investigated the alkaloids of the stem bark of Strychnos soubrenszs Hutch. et Dah.Strychnos soubvenszs (1) (section Lanigerae) is a liana or scandent shrub, 10-50 m long, up to 40 m high, climbing in trees. It is widely distributed in the West African rain or secondary forests, often on river banks, at altitudes of 0-1000 m. The bark is pale grey to dark brown with large lenticels.Preliminary phytochemical ( 2 ) and pharmacological (3,4) studies revealed that the small amount of alkaloids present (

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supporting

confidence: 64%

Alkaloids of Strychnos soubrensis

Ohiri¹,

Verpoorte²,

Svendsen³

et al. 1983

J. Nat. Prod.

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“…In particular, the methyl group at C-8 shields the C-4 proton (A6 -0.36) and deshields the C-4 carbon (A6 5.8) of 44, and conversion of 44 and 45 results in a shielding of the C-4 proton ( 4 6 -0.52) and a deshielding of C-4 itself (A6 2.9). Analogy for the former effect is found in the effect of the C-8 methyl group in the tricyclic lactone 47 on the chemical shifts of the C-4 proton (A6 -0.50) and of C-4 ( 4 6 6.5) of the parent lactone 4 (2,27). Again the ir spectrum of the periodic acid product 4b shows the presence of a cyclopentanone rather than a cyclohexanone moiety.…”

mentioning

confidence: 65%

Tandem Wessely oxidation and intramolecular Diels–Alder reactions. III. Synthesis of isotwistanes

Yates¹,

Macas²

1988

Can. J. Chem.

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PETER YATES and TADAS S. MACAS. Can. J. Chem. 66, 1 (1988).Wessely oxidation of o-(3-alkenyl) phenols (5) with lead tetraacetate gives 6-acetoxy-6-(3-atkeny1)-2,4-cyclohexadien-I-ones (6), which undergo intramolecular Diels-Alder reactions to give isotwistene (hexahydro-1.5-methanoindene) derivatives (7). These, on hydrolysis followed by oxidation with periodic acid, give hexahydro-1-0x0-l H-indene-5-carboxylic acids (41, 46). Compounds 5 were prepared either by Grignard coupling of o-methoxybenzyl chloride with ally1 halides followed by de-0-methylation with sodium thioethoxide or via reduction of dihydrocoumarins (18-20) to 2-chromanols (21-23) with diisobutylaluminum hydride, followed by Wittig reaction of these with ethyl (triphenylphosphoranylidene)acetate. The oxidation of ortho-substituted phenols with lead tetraacetate LTA to give 6-acetoxy-2,4-cyclohexadien-1-ones (oquinol acetates; I ) , which was first reported by Wessely and his co-workers in 1950 (4), is the simplest general method for the synthesis of the latter class of compounds. Wessely early recognized (5) the potential utility of o-quinol acetates in intermolecular Diels-Alder reactions leading to bicyclo[2.2.2]octenones and bicyclo[2.2.2]octadienones (e.g., 2 (R = CH3) 3, (Scheme 1).Work in these laboratories (1, 2) has shown that an intramolecular version of the latter reaction can be effected by Wessely oxidation products that incorporate a dienophilic group in the ester moiety (e.g., 3). This provides a route to tricyclic lactones of type 4, as exemplified in Scheme 2.It occurred to us that a related reaction sequence involving Wessely oxidation of an o-(3-alkenyl) phenol (5) to give a 2,4-cyclohexadienone of type 6, followed by intramolecular cyclic analogues of 4, i.e., isotwistene (hexahydro-l,5-methanoindene) derivatives of type 7 (Scheme 3). Other workers (7) have already demonstrated the practicability of the synthesis of tricyclic systems via intramolecular reactions of alkenyl 1,3-cyclohexadiene derivatives, but none to our knowledge has coupled this reaction with the Wessely oxidation reaction. Can. J. Chem. Downloaded from www.nrcresearchpress.com by 54.213.91.117 on 05/10/18For personal use only.

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“…The introduction of AS B.7-unsaturation into 2-norbornanones has been observed preiiobsly to lead to shielding of the carbonyl carbon; it has also been observed that C-6 is shielded and C-5 is deshielded with respect to the corresponding olefins (29). These effects have been attributed in part to homoconjugation (37). Introduction of a second P,y ethylenic bond as in 18 can be seen to lead to appreciable further deshielding of the carbonyl carbon, perhaps as a result of "cross-homoconjugation".…”

Section: C Nuclear Magnetic Resonance Spectramentioning

confidence: 98%

Aliphatic diazo compounds. XIV. The synthesis of 7-substituted 3-diazo-2-norbornanones and the infrared and proton and carbon-13 nuclear magnetic resonance spectra of these diazo ketones and their precursors

Yates¹,

Kronis²

1984

Can. J. Chem.

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. 62, 1751 (1984).syn-and anti-7-lsopropyl-2-norbornanone (5 and 6) were prepared by catalytic hydrogenation of 7-isopropylidene-2-norbornanone; syri-and anti-7-benzhydryl-2-norbornane (9 and 10) were prepared in analogous fashion. Kctones 5 and 6 and syrl-and arlti-7-tert-butyl-2-norbornanone (7 and 8) were converted to the corresponding 3-diazo-2-norbornanones 1-4 via the monotosylhydrazones 44-47 of the corresponding a-diketones 40-43. The 'H and "C nmr spcctra of 1-10,40-47, and thcir precursors have been analyzed. The 'H nmr spectra of the diazo ketones 1-4 have their C-I and C-4 bridgehead proton signals shifted to higher and lower field, respectively, relative to the bridgehead signals of thc corresponding dikctones. Thc "C nmr spectra of all pairs of bicyclic epimers shown y-garrche shielding effects by the 7-substitucnt at (sp3) C-3 in thc syrl compounds and at C-5 and C-6 in the arlti compounds. A converse effect is found at (sp') C-2 (and C-3 in the diketoncs). Comparison of the magnitude of the shielding effects of C-7 methyl, isopropyl, benzhydryl, and tert-butyl substituents gives evidence of 6 deshielding effects at C-3 in the syrl compounds and at C-5 and C-6 in thc onti compounds by methyl substitucnts on C-8.PETER YATES et JOHN DAVID KRONIS. Can. J. Chem. 62, 1751 (1984.On a prCparC Ics isopropyl-7 norbornanones-2 syrl et anti (5 et 6) par hydrogenation catalytique de I'isopropylidene-7 norbornanone-2; on a prCparC les benzhydryl-7 norbornanones-2 syrl et nrlti (9 et 10) d'unc manikre semblablc. On a transform6 les cCtones 5 et 6 ainsi que les tert-butyl-7 norbornanones-2 sytl et anti (7 et 8) en leurs diazo-3 norbornanones-2 correspondantes (1-4) par le biais des monotosylhydrazones 44-47 des a-dicCtones correspondantes 40-43. On a analysC les spectrcs rmn du ' H et du "C des composCs 1-10 et 40-47 et de leurs prCcurseurs. Dans les spectres rmn du 'H des diazocCtones 1-4, les signaux des protons en tCte de pont (C-l et C-4) sont dCplacCs respectivcment vers des champs plus haut et plus bas, par rapport aux signaux des protons dans les positions Cquivalentes des dicttones correspondantes. Les spectrcs rmn du '.'c de chacune des paires d'Cpimkres bicycliques prtsentent tous des effets de blindage y-gauche, dus aux substituants en position 7 et affectant la position C-3 (sp3) des composCs syrl et les positions C-5 et C-6 dcs composts anti. On observe un effet inverse au niveau de C-2 (sp') (et de C-3 dans les dicttones). Une comparaison de I'amplitude dcs cffets de blindage provoquCs par les substituants mCthyle, isopropyle, benzhydrylc et tert-butyle en C-7 suggkre que les substituants mCthyles cn C-8 provoquent des effets de dtblindage 6 en C-3 dans les composCs syn et en C-5 et C-6 dans les composCs anti.[Traduit par le journal]In connection with our studies on the acid-catalyzed decomposition of a-diazo ketones (1, 2), we required pairs of 3-diazo-2-norbornanones with bulky syt7-and anti-7 substituents. We describe here the synthesis of the diazo ketones 1-4, prepared for this purpose, and di...

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Carbonyl carbon chemical shifts in the 13c spectra of cyclic ketones

Cited by 21 publications

References 47 publications

Alkaloids of Strychnos soubrensis

Alkaloids of Strychnos soubrensis

Tandem Wessely oxidation and intramolecular Diels–Alder reactions. III. Synthesis of isotwistanes

Aliphatic diazo compounds. XIV. The synthesis of 7-substituted 3-diazo-2-norbornanones and the infrared and proton and carbon-13 nuclear magnetic resonance spectra of these diazo ketones and their precursors

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