Study of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">K</mml:mi></mml:mrow><mml:mrow><mml:mn>39</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mo>(</mml:mo><mml:mi>d</mml:mi><mml:mo>,</mml:mo><mml:mi> </mml:mi><mml:mrow><mml:msup><mml:mrow><mml:mi>d</mml:mi></mml:mrow><mml:mrow><mml:mo>′</mml:mo></mml:mrow></mml:msup></mml:mrow><mml:mo>)</mml:mo></mml:math>Reaction

Hamburger, Ernst Wolfgang; Reber, L.H.

doi:10.1103/physrev.128.333

Cited by 29 publications

(21 citation statements)

References 20 publications

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“…Therefore, suitable radical precursors for 5-and 6-exo cyclisation were prepared (Scheme 2). The 5-membered ring cyclisation with the precursor 16 using Bu 3 SnH gave only the reduced uncyclised product 19 (Scheme 3). Even syringe pump addition of Bu 3 SnH, with either Et 3 B (r.t.) or AIBN (110 • C) as initiators, gave only 19.…”

Section: Aryl Radical Cyclisationmentioning

confidence: 99%

“…This possibility was eliminated by repeating the reaction with Bu 3 SnD which gave only deuteriation on the aryl Scheme 2 Reagents and conditions: i, tert-BuOK, DMF, 63% (16 from 14), 38% (17 from 15). 3 B, PhMe, r.t., Bu 3 SnH (fast addition) 96% (19), slow addition, 30% (19); AIBN, Bu 3 SnH (slow addition), PhMe, reflux, 45% (19); Et 3 B, TTMSS, 35% (19); (Me 3 Sn) 2 , tert-BuPh, reflux, 18% (20), 65% (19). radical position, and none on the 2-position of the quinazolinone, and these results indicated that the rate of cyclisation was not favourable compared to reduction with Bu 3 SnH.…”

Section: Aryl Radical Cyclisationmentioning

confidence: 99%

“…The general procedure for Bu 3 SnH reactions using Et 3 B as initiator was repeated except that Bu 3 SnH was added by a syringe pump over 6 h to give 3-benzyl-3H-quinazolin-4-one 19 (30%).…”

Section: Experimental Generalmentioning

confidence: 99%

“…A precipitate of polymeric dimethyltin was produced. The product was eluted with ethyl acetate and further worked-up as for the general procedure for Bu 3 19 (2 H, s, CH 2 ), 7.28-7.35 (3 H, m) 139.6 (C), 149.4 (C), 154.9 (C) and 160.5 (C). The data were the same as that in the literature.…”

Section: Experimental Generalmentioning

confidence: 99%

“…22,29, 30 However, the lower aromaticity in the pyrrole ring of indole, facilitates both reductive and oxidative cyclisation depending on the conditions. 11,12, 31 The radical intermediate 10, whether a p-radical or not, is still a strongly stabilised anilyl radical and therefore the rate of reduction by Bu 3 SnH to yield 12 is probably too low to be competitive with loss of hydrogen to yield the 'oxidised' product. The reactions could also be regarded as exo-cyclisations onto imines which are well known.…”

mentioning

confidence: 99%

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Radical reactions with 3H-quinazolin-4-ones: synthesis of deoxyvasicinone, mackinazolinone, luotonin A, rutaecarpine and tryptanthrin

et al. 2007

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Alkyl, aryl, heteroaryl and acyl radicals have been cyclised onto the 2-position of 3H-quinazolin-4-one. The side chains containing the radical precursors were attached to the nitrogen atom in the 3-position. The cyclisations take place by aromatic homolytic substitution hence retain the aromaticity of the 3H-quinazolin-4-one ring. The highest yields were obtained using hexamethylditin to facilitate cyclisation rather than reduction without cyclisation. The alkaloids deoxyvasicinone 2, mackinazolinone 3, tryptanthrin 4, luotonin A 5 and rutaecarpine 8 were synthesised by radical cyclisation onto 3H-quinazolin-4-one.The 3H-quinazolin-4-one ring system is important to the biological activity of both naturally occurring alkaloids, biosynthesised from anthranilic acid, and pharmaceuticals. The alkaloids include vasicinone 1 and deoxyvasicinone 2, 1 mackinazolinone 3, 2 tryptanthrin 4, 3 luotonins A 5, B 6 and E 7 4 and rutaecarpine 8. 5 3H-Quinazolin-4-one alkaloids have been recently reviewed. 6 All the 3H-quinazolin-4-one natural products have interesting biological activity and have therefore been extensively investigated for useful pharmaceutical activity. The 3H-quinazolin-4-one ring is regarded as a 'privileged structure' in combinatorial synthesis. 7 These are structures which represent molecules that are capable of binding at multiple sites with high affinity and facilitate more rapid discovery of useful medicinally active compounds. 7Our study involved the development of protocols involving radical cyclisation for the synthesis of polycyclic 3H-quinazolin-3-ones (Scheme 1). The protocols have also been used for the synthesis of novel polycyclic quinazolinones including the natural Department of Chemistry, Loughborough University, Loughborough, Leics, UK LE11 3TU. E-mail: g.w.weaver@lboro.ac.uk; Fax: 44(0) 1509 223925; Tel: 44(0) All of the above cyclisations are 'oxidative' i.e. the intermediate p-radicals are not reduced by triorganometal hydrides [e.g. tributyltin hydyride (Bu 3 SnH)] as normally observed for these reagents. The cyclisations proceed by aromatic homolytic substitution with abstraction of hydrogen in a rearomatisation process. Aromatic homolytic substitution has been recently reviewed 27 and the mechanism of Bu 3 SnH mediated 'oxidative' cyclisation elaborated. 28 The pyrimidin-4-one ring of the quinazolin-4-ones has some aromaticity and therefore aromatic homolytic substitution could be predicted, and was observed in our studies, as shown in Scheme 1 (9 to 11 via the p-radical 10). However, the lower aromaticity could favour reductive cyclisation in which the intermediate p-radical 10 is intercepted by reagents such as Bu 3 SnH. Our prediction that radical cyclisation onto the quinazolin-4-one ring would be 'oxidative' was supported by the 'oxidative' radical cyclisation onto related ring systems, e.g. pyrimidine-2,4-diones, 23,24This journal is

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Section: Aryl Radical Cyclisationmentioning

confidence: 99%

Section: Aryl Radical Cyclisationmentioning

confidence: 99%

Section: Experimental Generalmentioning

confidence: 99%

Section: Experimental Generalmentioning

confidence: 99%

mentioning

confidence: 99%

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Radical reactions with 3H-quinazolin-4-ones: synthesis of deoxyvasicinone, mackinazolinone, luotonin A, rutaecarpine and tryptanthrin

et al. 2007

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The Elusive Indigo Precursors in Woad (Isatis tinctoria L.) – Identification of the Major Indigo Precursor, Isatan A, and a Structure Revision of Isatan B

Oberthür¹,

Schneider

Graf³

et al. 2004

Chemistry & Biodiversity

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A metabolite-profiling study of shock-frozen leaves of Isatis tinctoria L., an old indigo dye plant and medicinal herb, revealed a complex pattern of indigo-forming compounds with higher polarities than the known indigo precursors isatan B and indican. These highly unstable compounds underwent rapid post-harvest transformation and were not detected in air-dried leaves. The major indigo precursor, named isatan A (4), was isolated by rapid normal-phase and gel chromatography, along with isatan B (3). A full spectral data set of 3 showed that the previous structure assignment as 'indoxyl-5-ketogluconate' has to be revised to 1H-indol-3-yl beta-D-ribohex-3-ulopyranoside. Isatan A (4) was identified as 1H-indol-3-yl 6'-O-(carboxyacetyl)-beta-D-ribohex-3'-ulopyranoside. In aqueous solution, glycosides 3 and 4 occur as hydrates and undergo rapid hydrolysis under very mild acidic or basic conditions.

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Efficient Solid‐Phase Synthesis of Highly Functionalized 1,4‐Benzodiazepin‐5‐one Derivatives and Related Compounds by Intramolecular Aza–Wittig Reactions

Gil¹,

Bräse²

2005

Chemistry A European J

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Due to their widespread biological activities and favorable pharmacokinetic properties, benzodiazepines were among the first classes of small molecules to be synthesized on solid supports. Since then, there have been numerous reports on the synthesis of similar skeletons. We have employed the T1 triazene linker to yield 1,4-benzodiazepin-5-one. Starting from various substituted triazene resins, cleavage in the presence of an azide donor, such as trimethylsilylazide, gave rise to aryl azides. Intramolecular aza-Wittig reactions produced the appropriately functionalized N-heterocycles. By using this route, the natural product deoxyvasicinone and related compounds were prepared.

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Study of theK39(d, d′)Reaction

Cited by 29 publications

References 20 publications

Radical reactions with 3H-quinazolin-4-ones: synthesis of deoxyvasicinone, mackinazolinone, luotonin A, rutaecarpine and tryptanthrin

Radical reactions with 3H-quinazolin-4-ones: synthesis of deoxyvasicinone, mackinazolinone, luotonin A, rutaecarpine and tryptanthrin

The Elusive Indigo Precursors in Woad (Isatis tinctoria L.) – Identification of the Major Indigo Precursor, Isatan A, and a Structure Revision of Isatan B

Efficient Solid‐Phase Synthesis of Highly Functionalized 1,4‐Benzodiazepin‐5‐one Derivatives and Related Compounds by Intramolecular Aza–Wittig Reactions

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