Diels–Alder trapping of in situ generated dienes from 3,4-dihydro-2H-pyran with p-quinone catalysed by p-toluenesulfonic acid
01 Feb 2017-Organic and Biomolecular Chemistry (The Royal Society of Chemistry)-Vol. 15, Iss: 5, pp 1115-1121
TL;DR: This comprehensive study portrays that p-toluenesulfonic acid is a more efficient catalyst for the reaction between p-quinones and 3,4-dihydro-2H-pyran, than the Lewis acids.
Abstract: This comprehensive study portrays that p-toluenesulfonic acid is a more efficient catalyst for the reaction between p-quinones and 3,4-dihydro-2H-pyran, than the Lewis acids. The products were accomplished by the Diels–Alder cycloaddition reaction and their mechanistic pathways have been formulated. The impact of C2 and C2,5 substituents of the p-quinones on the cycloaddition reaction has been explored. Remarkably, it is the first report to explore this kind of in situ generated diene for the Diels–Alder cycloaddition reaction.
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TL;DR: In this paper, an efficient enantioselective construction of tetrahydronaphthalene-1,4-diones as well as dihydronaphthalene 1,4diols by a chiral phosphoric acid catalyzed quinone Diels-Alder reaction with dienecarbamates is reported.
Abstract: An efficient enantioselective construction of tetrahydronaphthalene-1,4-diones as well as dihydronaphthalene-1,4-diols by a chiral phosphoric acid catalyzed quinone Diels-Alder reaction with dienecarbamates is reported. The nature of the protecting group on the diene is key to the success of achieving high enantioselectivity. The divergent "redox" selectivity is controlled by using an adequate amount of quinones. Reversible redox switching without erosion of enantioselectivity was possible from individual redox isomers.
24 citations
TL;DR: Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields.
Abstract: Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process.
13 citations
TL;DR: In this article, a tricyclique de structure voisine de celle des precurseurs des podocarpanes, par cycloaddition du vinylcyclohexene avec l'acide benzoquinone-1,4 carboxylique, is presented.
Abstract: On prepare un compose tricyclique de structure voisine de celle des precurseurs des podocarpanes, par cycloaddition du vinylcyclohexene avec l'acide benzoquinone-1,4 carboxylique. On etudie la structure cristalline du compose et on explique par une etude theorique la stereochimie de la reaction
6 citations
References
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TL;DR: The first total synthesis of (+)-hatomarubigin 3 is described, where Sequential aromatization, photooxidation and hydrolysis of the glucosyl unit gave (+)-3 in an 8% overall yield from 8.
Abstract: The first total synthesis of (+)-hatomarubigin 3 is described. The tetra-O-acetyl diborate promoted Diels−Alder reaction of 5-hydroxy-8-(2‘,3‘,4‘,6‘-tetra-O-acetyl-β-d-glucopyranosyloxy)-1,4-naphthoquinone 8 and (E, 1R*,5R*)-3-(2‘-methoxyvinyl)cyclohex-2-enol (±)-7 gave a mixture of four cycloadducts from which (1S,3S,6S,6aR,12aR,12bS)-1,8-dihydroxy-6-dimethoxy-1-hydroxy-3-methyl-11-(2‘,3‘,4‘,6‘-tetra-O-acetyl-β-d-glucopyranosyloxy)-1,2,3,4,6,6a,12a,12b-octahydrobenz[a]anthracene-7,12-dione 12 was isolated in 51% yield. Selective methylation and acetylation of 12 gave (1S,3S,6S,6aR,12aR,12bS)-1-acetoxy-6,8-dimethoxy-3-methyl-11-(2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyloxy)-1,2,3,4,6,6a,12a,12b-octahydrobenz[a]anthracene-7,12-dione 10a. Sequential aromatization, photooxidation and hydrolysis of the glucosyl unit gave (+)-3 (98% ee) in an 8% overall yield from 8.
19 citations
TL;DR: Results can suggest that compound 2-methoxy-6-n-pentyl-hydroquinone-di-(2'-tetrahydropyranyl) ether may act as a prodrug with some advantages in comparison with the Primin, which has shown antimicrobial and antitumour properties.
Abstract: Cancer is a serious worldwide health threat, killing almost seven million people per year. Quinones are an important class of antitumour agents that are activated by tumour hypoxia. Primin (2-methoxy-6-n-pentyl-1,4-benzoquinone), a naturally-occurring product obtained from Primula obconica (Primulaceae) has shown antimicrobial and antitumour properties. The synthesis of the Primin to obtain 3-, 5- or 6-alkyl substituted derivatives has been previously attempted seeking antitumour activity. The intermediate reaction products, 2-methoxy-hydroquinone-di-(2-tetrahydropyranyl) ether and 2-methoxy-6-n-pentyl-hydroquinone-di-(2-tetrahydropyranyl) ether were obtained and evaluated against sarcoma 180 (S-180) and Ehrlich carcinoma, as well as toxicity tests were performed. The antitumour activity tests showed that these intermediate compounds were able to inhibit S-180 sarcoma and Ehrlich carcinoma growth in mice. These results indicated that the tetrahydropyranyl protect group conserved the antitumour activity in comparison with quinone group, however, it exhibited a less toxic effect, with no characteristic of quinones. These results can suggest that compound 2-methoxy-6-n-pentyl-hydroquinone-di-(2-tetrahydropyranyl) ether may act as a prodrug with some advantages in comparison with the Primin.
10 citations
TL;DR: Improved regioselectivity in catalyzed Diels-Alder cycloadditions between non-symmetrical benzoquinones and mono-substituted butadienes is achieved by use of SbCl5 as mentioned in this paper.
9 citations
TL;DR: In this article, a tricyclique de structure voisine de celle des precurseurs des podocarpanes, par cycloaddition du vinylcyclohexene avec l'acide benzoquinone-1,4 carboxylique, is presented.
Abstract: On prepare un compose tricyclique de structure voisine de celle des precurseurs des podocarpanes, par cycloaddition du vinylcyclohexene avec l'acide benzoquinone-1,4 carboxylique. On etudie la structure cristalline du compose et on explique par une etude theorique la stereochimie de la reaction
6 citations
TL;DR: The asymmetric Diels-Alder reaction between 2-(E-2-acetoxyvinyl)-8-tert-butyl-3,4-dihydronaphthalene (8) and enantiopure (SS)-2-(p-tolylsulfinyl)-1,4
Abstract: The asymmetric Diels−Alder reaction between 2-(E-2-acetoxyvinyl)-8-tert-butyl-3,4-dihydronaphthalene (8) and enantiopure (SS)-2-(p-tolylsulfinyl)-1,4-benzoquinone (1) takes place exclusively on the unsubstituted C5−C6 double bond of (SS)-1 with a very high control of the chemo-, regio-, and diastereoselectivity of the process affording tetracyclic sulfinyl derivative 13a possessing five stereogenic centers. The analogue diene 9, lacking the tert-butyl group, gave a less chemoselective reaction (C2−C3/C5−C6: 60/40) in favor of reaction through the sulfoxide-substituted double bond C2−C3 of 1. Steric effects of the remote tert-butyl group and electronic factors due to the OAc substituent are controlling the process.
5 citations