The Dimerization of Chiral Allenes: Pairs of Enantiomers and Pairs of Homomers Furnish Different Diastereomers

Christl, Manfred; Groetsch, Stefan; Günther, Kurt

doi:10.1002/1521-3773(20000915)39:18<3261::aid-anie3261>3.0.co;2-t

Cited by 21 publications

(24 citation statements)

References 11 publications

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“…Other examples are provided by the thermolysis of the 1,2‐bismethylenecyclobutane derivatives produced at low temperatures upon dimerisation of triphenylallene20 and 1‐(2,2′‐biphenylylen)‐3‐phenylallene 17. Heretofore, only one case has been documented that describes the isolation of a primary product resulting from the attack of a radical centre of a phenyl‐substituted tetramethyleneethane diradical at the phenyl group of the second molecule half, that is, the dimer 20 of racemic 1‐phenyl‐1,2‐cyclooctadiene ( 19 ), which was generated from racemic 8,8‐dibromo‐1‐phenylbicyclo[5.1.0]octane ( 18 ; Scheme ) 16. 21…”

Section: Resultsmentioning

confidence: 99%

“…The first two steps from 2 en route to 16 and 17 should be analogous to the pathway proposed for the conversion of 19 into 20 16. 21 Thus, two molecules of 2 should combine to give the tetramethyleneethane diradical 21 , which then does not undergo the standard reaction of such species with formation of a 1,2‐bismethylenecyclobutane derivative,1 but collapses by bond formation of a phenyl‐bearing allyl‐radical terminus with the phenyl group of the second molecule half furnishing the 1‐methylene‐2,4‐cyclohexadiene derivative 22 (Scheme ).…”

Section: Resultsmentioning

confidence: 99%

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Reduction of job loss in persons with rheumatic diseases receiving vocational rehabilitation: A randomized controlled trial

Allaire

LaValley

2003

Arthritis & Rheumatism

113

128

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Objective. Job loss is a major consequence of rheumatic diseases, and clinicians may refer patients to vocational rehabilitation for help. When provided after job loss, the impact of vocational rehabilitation is short term. This randomized controlled trial with 48 months of followup was undertaken to determine the efficacy of vocational rehabilitation provided to persons with rheumatic diseases while they are still employed, but at risk for job loss.Methods. A total of 242 patients with rheumatic diseases residing in Massachusetts were recruited through their rheumatologists for study. Participants were randomly assigned to the experimental group (n ‫؍‬ 122) or the control group (n ‫؍‬ 120). Subjects in the experimental group received two 1.5-hour sessions of vocational rehabilitation; those in the control group received print materials about disability employment issues and resources by mail. The main outcome assessed was the time to first job loss. Job losses were defined as permanent disability, premature retirement, or a period of unemployment. All analyses were conducted on an intent-to-treat basis.Results. Job loss was delayed in the experimental group compared with the control group (P ‫؍‬ 0.03 by log rank test). After adjustment for confounders, participation in the experimental group was found to be protective against job loss (odds ratio 0.58 [95% confidence interval 0.34-0.99], P ‫؍‬ 0.05 by pooled logistic regression).Conclusion. Vocational rehabilitation delivered to patients at risk for job loss, but while they were still employed, delayed job loss. Such an intervention has the potential to reduce the high indirect costs, as well as the personal impact, of rheumatic diseases.Health-related job loss is a major consequence of rheumatic diseases. In the most recent analyses (1), costs stemming from lost wages, so-called indirect costs, for all forms of arthritis were 74% of the total costs, while the direct costs of medical care were 26% of the total. This burden can be expected to increase because the portion of the US work force that is 55 years of age and older is increasing (by 2020, it will account for one-fifth of the work force) (2) and because the incidence and prevalence of many rheumatic diseases rise substantially after age 50 years. Health-related job loss also exacts a substantial toll on the quality of life of individuals, being associated with lower levels of self-esteem, life satisfaction, adaptation, perceived health status, and in those with rheumatoid arthritis, higher levels of depression and pain (3-5).Vocational rehabilitation is one approach to addressing health-related job loss. Rheumatologists and other clinicians may wish to refer their patients with rheumatic diseases to vocational rehabilitation for help. However, there is a shortage of studies evaluating the effectiveness of vocational rehabilitation. Studies that have been done suggest that while it can be effective in helping persons with disabilities regain employment, this effect is often short-lived (6). Moreover, the...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Reduction of job loss in persons with rheumatic diseases receiving vocational rehabilitation: A randomized controlled trial

Allaire

LaValley

2003

Arthritis & Rheumatism

113

128

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“…Surprisingly, we have observed that under neat conditions, 1,3‐diphenyl allene 7cea undergoes cyclodimerization even at 25 °C in 24 h. Thus, whereas the freshly prepared pure chiral allene 7cea sample exhibits an [ α ] D 25 = –830 ( c = 0.53, CHCl 3 ), the value becomes zero when the product was kept at 25 °C for 72 h. The 13 C NMR spectrum of the product mixture indicates the presence of the cyclodimerized products 16e. We have also found that when freshly prepared pure chiral 1,3‐diphenylallene 7cea was stored in CDCl 3 solution, new signals corresponding to the cyclodimerized products started appearing in the 13 C NMR spectrum in 24 h at 25 °C 17…”

Section: Resultsmentioning

confidence: 82%

Zinc Salt Promoted Diastereoselective Synthesis of Chiral Propargylamines Using Chiral Piperazines and Their Enantioselective Conversion into Chiral Allenes

et al. 2014

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Zinc chloride catalyzed reactions of chiral piperazine derivatives 4a–d with 1‐alkynes and aldehydes give chiral propargylamines in 67–95 % yields with up to 99:1 dr. The chiral propargylamines are converted into chiral allenes by using zinc bromide in short reaction times (1–2 h) in high enantioselectivities (up to 99 % ee) in good yields (up to 89 %). The chiral piperazines are recovered in good yields (79–86 %) by reduction of the imine byproducts in situ by using NaBH4. Unexpectedly, the chiral aryl‐substituted allenes undergo facile cyclodimerization under neat conditions at 25 °C, in contrast to an earlier report that cyclodimerization takes place at 80 °C in benzene, which further illustrates the importance of the two‐step procedure reported herein because the chiral propargylamine may be converted into chiral allene when required.

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“…Indeed, the mechanism of sequential formation of these isomers has been rationalized in terms of homolysis of the C(3)eC(4) bond in 2 to generate a tetramethylene-ethane diradical, which can exist in three isomeric forms: endo,endo, endo,exo and exo,exo, where endo and exo refer to the orientations of the phenyl substituents relative to the two allyl fragments, as depicted in Scheme 2. 8 Now, following the allene dimerization mechanism proposed by Christl, 13 conrotatory ring closure of the endo, endo form leads to the trans isomer 3, while at successively higher temperatures exo,endo and exo,exo diradicals lead to the cis and trans products 4 and 5, respectively.…”

Section: Introductionmentioning

confidence: 84%

C2-Symmetric 1,2-di(fluorenylidene)cyclobutanes: syntheses, structures, rearrangements and reactivity

et al. 2015

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The Dimerization of Chiral Allenes: Pairs of Enantiomers and Pairs of Homomers Furnish Different Diastereomers

Abstract: Treatment of the pure enantiomer 1 with methyllithium furnishes via cycloallene 2 its dimer 3 with high selectivity. In contrast, racemic 1 yielded only 5 % of 3 and 95 % of the cis isomer of 3. Thus, racemic 2 is an example of molecular recognition of remarkable selectivity.

Cited by 21 publications

References 11 publications

Reduction of job loss in persons with rheumatic diseases receiving vocational rehabilitation: A randomized controlled trial

Reduction of job loss in persons with rheumatic diseases receiving vocational rehabilitation: A randomized controlled trial

Zinc Salt Promoted Diastereoselective Synthesis of Chiral Propargylamines Using Chiral Piperazines and Their Enantioselective Conversion into Chiral Allenes

C2-Symmetric 1,2-di(fluorenylidene)cyclobutanes: syntheses, structures, rearrangements and reactivity

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