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Christl, Manfred; Groetsch, Stefan

doi:10.1002/(sici)1099-0690(200005)2000:10<1871::aid-ejoc1871>3.3.co;2-v

Cited by 15 publications

(27 citation statements)

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“…[21] As to the intermediate 4, the key question is why we did not observe one of its cycloadducts on treatment of 6 with KOtBu in the presence of [18]crown-6 and furan. The activation of KOtBu by [18]crown-6 has already been utilised for the generation of cycloallenes, such as 2, [10] cyclohexa-1,2,4-triene [6] and 3δ 2 -1H-naphthalene. [7] In two [7,10] out of the of three cases, cycloadducts of the intermediates with activated olefins were isolated, which inclines us to assume that we would have detected furan adducts of 4 had they been formed.…”

Section: Methodsmentioning

confidence: 99%

“…Our contributions to the field of six-membered cycloallenes have the principal goal of trapping species with a fleeting existence with activated olefins, thus giving cycloadducts; their main results have been summarized in two reviews. [1,2] In two more recent studies, we have investigated reactions undergone by cyclohexa-1,2,4-triene [6] and 3δ 2 -1H-naphthalene [7] in addition to cycloadditions with activated olefins. [8] The symmetrical (1) [9] and the unsymmetrical isopyran (2) [10Ϫ12] (Scheme 1) have been generated and characterised by trapping products.…”

Section: Introductionmentioning

confidence: 99%

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1-Methyl-1-azacyclohexa-2,3-diene(N−B)borane − Generation and Interception of an Unsymmetrical Isodihydropyridine

et al. 2001

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Keywords: Allenes / Amines / Boranes / Cycloadditions / Eliminations / Strained molecules 3-Bromo-1-methyl-1,2,5,6-tetrahydropyridine(N−B)borane (7) was prepared from 3-bromopyridine by conversion to 3-bromo-1-methylpyridinium iodide, hydrogenation of the latter with sodium tetrahydroborate and treatment of the resulting 3-bromo-1-methyl-1,2,5,6-tetrahydropyridine (6) with borane−dimethyl sulfide. Whereas no trapping product of the possible intermediate 1-methyl-1-azacyclohexa-2,3-diene (4) could be observed on treatment of 6 with potassium tert-but-

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

1-Methyl-1-azacyclohexa-2,3-diene(N−B)borane − Generation and Interception of an Unsymmetrical Isodihydropyridine

et al. 2001

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“…[6±8] The role of allene 6 and biradical 7 is, however, unclear. [9,10] At higher temperatures, processes including the intermediates 5 and 8 are more favorable; this is indicated by the increased formation of pentafulvene as a by-product. [11±15] With respect to the formation of fullerene-like moieties or building blocks, the effect of benzannelation on the barriers and enthalpies of formation is also important.…”

Section: Introductionmentioning

confidence: 99%

The Cyclization of Parent and Cyclic Hexa-1,3-dien-5-ynes—A Combined Theoretical and Experimental Study

et al. 2001

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The thermal cycloisomerization of both parent and benzannelated hexa-1,3-dien-5-yne, as well as of carbocyclic 1,3-dien-5-ynes (ring size 7-14), was investigated by using pure density functional theory (DFT) of Becke, Lee, Yang, and Parr (BLYP) in connection with the 6-31G* basis set and the Brueckner doubles coupled-cluster approach [BCCD(T)] with the cc-pVDZ basis set for the parent system. The initial cyclization product is the allenic cyclohexa-1,2,4-triene (isobenzene), while the respective biradical is the transition structure for the enantiomerization of the two allenes. Two consecutive [1,2]-H shifts further transform isobenzene to benzene. For the benzannelated system, the energetics are quite similar and the reaction path is the same with one exception: the intermediate biradical is not a transition state but a minimum which is energetically below isonaphthalene. The cyclization of the carbocyclic 1,3-dien-5-ynes, which follows the same reaction path as the parent system, clearly depends on the ring size. Like the cyclic enediynes, the dienynes were found to cyclize to products with reduced ring strain. This is not possible for the 7- and 8-membered dienynes, as their cyclization products are also highly strained. For 9- to 11-membered carbocycles, all intermediates, transition states, and products lie energetically below the parent system; this indicates a reduced cyclization temperature. All other rings (12- to 14-membered) have higher barriers. Exploratory kinetic experiments on the recently prepared 10- to 14-membered 1,3-dien-5-ynes rings show this tendency, and 10- and 11-membered rings indeed cyclize at lower temperatures.

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“…by [2ϩ2] photocycloadditions of HB, [19] the relevant dirad-In the absence of HB, the generation of a triplet radicalical would not rearrange, but would rather undergo converion pair from 3 CA and toluene is unlikely, since, based on sion into an oxetane derivative. Therefore, the formation of 7 should proceed in a phenylsulfane [28] and electrophilic additions (H ϩ , AcOHg ϩ , manner different from that whereby the corresponding halogens) [29] to HB. 2.40 V vs. SCE [38] ), CA at the bicyclobutane system of HB would furnish prodthe Weller equation gives a ∆G ET value of ϩ13.8 kcal ucts of other types, as exemplified by the radical addition of mol Ϫ1 .…”

Section: Discussionmentioning

confidence: 99%

Photocycloadditions of Chloranil to Homobenzvalene, Norbornadiene, and Quadricyclane

Braun,

Christl,

Deeg

et al. 1999

Eur. J. Org. Chem.

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Cited by 15 publications

References 0 publications

1-Methyl-1-azacyclohexa-2,3-diene(N−B)borane − Generation and Interception of an Unsymmetrical Isodihydropyridine

1-Methyl-1-azacyclohexa-2,3-diene(N−B)borane − Generation and Interception of an Unsymmetrical Isodihydropyridine

The Cyclization of Parent and Cyclic Hexa-1,3-dien-5-ynes—A Combined Theoretical and Experimental Study

Photocycloadditions of Chloranil to Homobenzvalene, Norbornadiene, and Quadricyclane

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