Unusual traits of cis and trans-2,3-dibromo-1,1-dimethylindane on the way from 1,1-dimethylindene to 2-bromo-, 3-bromo-, and 2,3-dibromo-1,1-dimethylindene
| Autor: | David S. Stephenson, Ernst Lattke, Rudolf Knorr, Petra Böhrer, Jakob Ruhdorfer |
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| Jazyk: | angličtina |
| Rok vydání: | 2016 |
| Předmět: |
Stereochemistry
chemistry.chemical_element 010402 general chemistry 01 natural sciences Full Research Paper cis/trans stereochemistry lcsh:QD241-441 chemistry.chemical_compound lcsh:Organic chemistry Cyclopentene five-membered ring conformation lcsh:Science Tribromide NMR couplings Bromine 010405 organic chemistry Organic Chemistry Diastereomer indenes 0104 chemical sciences Chemistry base-free dehydrobromination chemistry Stereoselectivity lcsh:Q Cis–trans isomerism Vicinal |
| Zdroj: | Beilstein Journal of Organic Chemistry, Vol 12, Iss 1, Pp 1178-1184 (2016) Beilstein Journal of Organic Chemistry |
| ISSN: | 1860-5397 |
| Popis: | Do not rely on the widely accepted rule that vicinal, sp3-positioned protons in cyclopentene moieties should always have more positive 3J NMR coupling constants for the cis than for the trans arrangement: Unrecognized exceptions might misguide one to wrong stereochemical assignments and thence to erroneous mechanistic conclusions. We show here that two structurally innocent-looking 2,3-dibromo-1,1-dimethylindanes violate the rule by means of their values of 3J(cis) = 6.1 Hz and 3J(trans) = 8.4 Hz. The stereoselective formation of the trans diastereomer from 1,1-dimethylindene was improved with the tribromide anion (Br3−) as the brominating agent in place of elemental bromine; the ensuing, regiospecific HBr elimination afforded 3-bromo-1,1-dimethylindene. The addition of elemental bromine to the latter compound, followed by thermal HBr elimination, furnished 2,3-dibromo-1,1-dimethylindene, whose Br/Li interchange reaction, precipitation, and subsequent protolysis yielded only 2-bromo-1,1-dimethylindene. |
| Databáze: | OpenAIRE |
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