2833-20-7Relevant articles and documents
Highly selective synthesis of conjugated dienoic and trienoic esters via alkyne elementometalation - Pd-catalyzed cross-coupling
Wang, Guangwei,Mohan, Swathi,Negishi, Ei-Ichi
scheme or table, p. 11344 - 11349 (2011/10/30)
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 nBu4NF 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.
AN IMPROVED PROCEDURE FOR THE TWO CARBON HOMOLOGATION OF ESTERS TO α,β-UNSATURATED ESTERS
Takacs, James M.,Helle, Mark A.,Seely, Franklin L.
, p. 1257 - 1260 (2007/10/02)
Treatment of esters with diisobutylaluminium hydride (DIBAL) in the presence of lithio-trialkylphosphonoacetate results in improved yields of the homologated α,β-unsaturated esters.The problematic overreduction, which has previously observed in the half reduction of esters using DIBAL, is minimal (3percent) under these conditions.
