Highly selective synthesis of conjugated dienoic and trienoic esters via alkyne elementometalation–Pd-catalyzed cross-coupling
| Autor: | Swathi Mohan, Guangwei Wang, Ei-ichi Negishi |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2011 |
| Předmět: |
chemistry.chemical_classification
Multidisciplinary Esterification Molecular Structure Negishi coupling Alkyne Stereoisomerism Esters Conjugated system Alkenes Catalysis chemistry.chemical_compound chemistry Suzuki reaction Isomerism Models Chemical Alkynes Alkoxide Physical Sciences Organic chemistry Selectivity Palladium |
| Popis: | All four stereoisomers ( 7 – 10 ) of ethyl undeca-2,4-dienoate were prepared in ≥98% isomeric purity by Pd-catalyzed alkenylation (Negishi coupling) using ethyl ( E )- and ( Z )- β -bromoacrylates. Although the stereoisomeric purity of the 2 Z ,4 E -isomer ( 8 ) prepared by Suzuki coupling using conventional alkoxide and carbonate bases was ≤ 95%, as reported earlier, the use of CsF or n Bu 4 NF as a promoter base has now been found to give all of 7 – 10 in ≥98% selectivity. Other widely known methods reveal considerable limitations. Heck alkenylation was satisfactory for the syntheses of the 2 E ,4 E and 2 E ,4 Z isomers of ≥98% purity, but the purity of the 2 Z ,4 E isomer was ≤ 95%. Mutually complementary Horner–Wadsworth–Emmons and Still–Gennari (SG) olefinations are also of considerably limited scopes. Neither 2 E ,4 Z nor 2 Z ,4 Z isomer is readily prepared in ≥90% selectivity. In addition to (2 Z ,4 E )-dienoic esters, some (2 Z ,4 E ,6 E )- and (2 Z ,4 E ,6 Z )-trienoic esters have been prepared in ≥98% selectivity by a newly devised Pd-catalyzed alkenylation–SG olefination tandem process. As models for conjugated higher oligoenoic esters, all eight stereoisomers for ethyl trideca-2,4,6-trienoate ( 23 – 30 ) have been prepared in ≥98% overall selectivity. |
| Databáze: | OpenAIRE |
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