title: Highly selective synthesis of conjugated dienoic and trienoic esters via alkyne elementometalation-Pd-catalyzed cross-coupling.
abstract: 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 2Z,4E-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 2E,4E and 2E,4Z isomers of ≥ 98% purity, but the purity of the 2Z,4E isomer was ≤ 95%. Mutually complementary Horner-Wadsworth-Emmons and Still-Gennari (SG) olefinations are also of considerably limited scopes. Neither 2E,4Z nor 2Z,4Z isomer is readily prepared in ≥ 90% selectivity. In addition to (2Z,4E)-dienoic esters, some (2Z,4E,6E)- and (2Z,4E,6Z)-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.
authors.affiliation: H. C. Brown Laboratories of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2084, USA.
authors.forename: Guangwei
authors.initials: G
authors.lastname: Wang
authors.forename: Swathi
authors.initials: S
authors.lastname: Mohan
authors.forename: Ei-ichi
authors.initials: E
authors.lastname: Negishi
mesh_terms: D000475:Alkenes / Q000138:chemical synthesis* / Q000737:chemistry; D000480:Alkynes / Q000737:chemistry; D002384:Catalysis; D004951:Esterification; D004952:Esters / Q000138:chemical synthesis / Q000737:chemistry; D007536:Isomerism; D008956:Models, Chemical; D015394:Molecular Structure; D010165:Palladium; D013237:Stereoisomerism
chemical_list: D000475:Alkenes; D000480:Alkynes; D004952:Esters; D010165:Palladium