The first two-step 1,3-dipolar cycloadditions:  non-stereospecificity

Huisgen, Rolf; Mlostoń, Grzegorz; Langhals, Elke

doi:10.1021/ja00280a053

Cited by 112 publications

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“…These results have been taken as an evidence for a concerted process. Only few exceptions are known where the non stereospecific course of reaction suggests a stepwise mechanism [70]. Activation and reaction volumes were measured for few reactions of diazoalkanes, nitrones, and alkyl azides as dipoles with electron-deficient or neutral alkenes as dipolarophiles already in the early 1980 s. They are generally in the range of ∆V ≠ = -(21 ± 3) cm 3 mol -1 and ∆V = -(25 ± 2) cm 3 mol -1 [71].…”

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confidence: 99%

The Effect of Pressure on Organic Reactions

Klärner¹,

Wurche²

2000

J. prakt. Chem.

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The utility of high pressure for the understanding of chemical reactions and its application in organic synthesis is shown for cycloadditions (inter‐ and intramolecular Diels‐Alder reactions, 1,3‐dipolar and [2+2] cycloadditions), cheletropic reactions and pericyclic rearrangements (Cope and Claisen rearrangements and electrocyclizations). The origin of the effect of pressure on chemical reactions is discussed. Especially, the change in the packing coefficient during cyclization of chains and the effect of electrostriction on reactions, in which charged species are generated, contribute substantially to a volume contraction leading to a powerful pressure‐induced acceleration of such reactions. Finally, the effect of pressure on free‐radical reactions (homolytic bond dissociations and quinone oxidations) is described.

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confidence: 99%

The Effect of Pressure on Organic Reactions

Klärner¹,

Wurche²

2000

J. prakt. Chem.

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“…Especially important are reactions with 1,1-dimethoxybuta-1,3-diene [20] and sterically crowded thiocarbonyl ylides [21], which were established to occur stepwise via intermediate zwitterions. To the best of our knowledge, apart from thiocarbonyl ylides, the only other 1,3-dipoles used in reactions with 7 were diazo compounds [22], and the addition with di(tert-butyl)diazomethane was also shown to occur stepwise [23].…”

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confidence: 99%

Thermal [2+3]‐Cycloadditions of trans‐1‐Methyl‐2,3‐diphenylaziridine with CS and CC Dipolarophiles: An Unexpected Course with Dimethyl Dicyanofumarate

Mlostoń

Urbaniak

Domagała³

et al. 2009

Helvetica Chimica Acta

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The thermal reaction of trans-1-methyl-2,3-diphenylaziridine (trans-1a) with aromatic and cycloaliphatic thioketones 2 in boiling toluene yielded the corresponding cis-2,4-diphenyl-1,3-thiazolidines cis-4 via conrotatory ring opening of trans-1a and a concerted [2 þ 3]-cycloaddition of the intermediate (E,E)-configured azomethine ylide 3a (Scheme 1). The analogous reaction of cis-1a with dimethyl acetylenedicarboxylate (5) gave dimethyl trans-2,5-dihydro-1-methyl-2,5-diphenylpyrrole-3,4-dicarboxylate (trans-6) in accord with orbital-symmetry-controlled reactions (Scheme 2). On the other hand, the reactions of cis-1a and trans-1a with dimethyl dicyanofumarate (7a), as well as that of cis-1a and dimethyl dicyanomaleate (7b), led to mixtures of the same two stereoisomeric dimethyl 3,4-dicyano-1-methyl-2,5-diphenylpyrrolidine-3,4-dicarboxylates 8a and 8b (Scheme 3). This result has to be explained via a stepwise reaction mechanism, in which the intermediate zwitterions 11a and 11b equilibrate (Scheme 6). In contrast, cis-1,2,3-triphenylaziridine (cis-1b) and 7a gave only one stereoisomeric pyrrolidine-3,4-dicarboxylate 10, with the configuration expected on the basis of orbital-symmetry control, i.e., via concerted reaction steps (Scheme 10). The configuration of 8a and 10, as well as that of a derivative of 8b, were established by X-ray crystallography.

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“…Reflections on the consequences of the FMO model for concerted or stepwise cycloadditions suggested to him that the cycloaddition of a thiocarbonyl S-methylide to very electron-deficient dipolarophiles might induce a two-step cycloaddition, presumably via a zwitterionic intermediate. It is of no surprise that he was the first to find experimental evidence of such a cycloaddition [81]. A bulky substituent at one side of the thiocarbonyl S-methylide was assumed to support the formation of an open intermediate, a zwitterion.…”

Section: Scheme 24mentioning

confidence: 99%