Clean Inversion of Configuration in the Pd-Catalyzed Cross-Coupling of 2-Bromo-1,3-dienes
摘要:
The Pd-catalyzed cross-coupling reaction of 2-bromo-1,3-dienes derived from alkyl aldehydes, especially with Cl2Pd(DPEphos) as a catalyst, proceeds with clean stereoinversion of the Br-bearing C=C bond to produce in high yields and in high stereoselectivity (>/=97-98%) conjugated Z,E dienes of potentially high utility in the synthesis of complex natural products. The observed stereoinversion cannot be readily accommodated by the widely accepted pi-sigma-pi rearrangement mechanism for isomerization of ordinary allylpalladium derivatives.
Search for Highly Efficient, Stereoselective, and Practical Synthesis of Complex Organic Compounds of Medicinal Importance as Exemplified by the Synthesis of the C21C37 Fragment of Amphotericin B
Highly stereoselective: A highly efficient, stereoselective and practicalsynthesis of the C21C37 fragment of amphotericin B was realized in 25 % overall yield in eight longest linear steps from commercially available ethyl (S)‐3‐hydroxybutyrate by using Fráter–Seebach alkylation, Brown crotylboration, Negishi coupling, Heck reaction, and Horner–Wadsworth–Emmons (HWE) olefination as key steps (see
The effect of vicinyl olefinic halogens on cross-coupling reactions using Pd(0) catalysis
作者:Michael G. Organ、Haleh Ghasemi、Cory Valente
DOI:10.1016/j.tet.2004.08.006
日期:2004.10
products reliably under all reaction conditions. Compound 5 did not provide cross coupled products under any of the reaction conditions used. The Negishi reaction was the only one that worked for templates 4 and 11. Studies indicate that oxidative addition of the most reactive carbon–halogenbond to Pd(0) is followed by elimination of the second halide, when the second halide is a bromide or an iodide
A Novel, Selective, and Efficient Route to Carotenoids and Related Natural Products via Zr-Catalyzed Carboalumination and Pd- and Zn-Catalyzed Cross Coupling
作者:Fanxing Zeng、Ei-ichi Negishi
DOI:10.1021/ol000384y
日期:2001.3.1
stereoselective protocol for the syntheses of symmetrical and unsymmetrical carotenoids involving Zr-catalyzed carboalumination of conjugated oligoenynes and Pd- and Zn-catalyzed alkenyl-alkenyl coupling has been developed and applied to the syntheses of beta- and gamma-carotene and vitamin A. gamma-Carotene of > or =99% isomeric purity was prepared in three linear steps (five steps overall) from beta-ionone
Strictly “Pair”-Selective and Economical Synthesis of Conjugated Diynes via Pd-Catalyzed Reaction of Terminal Alkynes with 1,1-Dichloroethylene, Elimination with LDA, and Subsequent Transformations
作者:Mingxing Qian、Ei-ichi Negishi
DOI:10.1021/op034029+
日期:2003.5.1
Various unsymmetrically substituted conjugateddiynes can be synthesized in a completely “pair”-selective manner via Pd-catalyzed reaction of terminal alkynes with 1,1-dichloroethylene in the presence of Pd(PPh3)4 followed by elimination with 2 equiv of lithium diisopropylamide (LDA), zincation with ZnBr2 or ZnCl2, and Pd-catalyzed cross-coupling with aryl and alkenyl iodides and bromides. The desired
Highly Satisfactory Alkynylation of Alkenyl Halides via Pd-Catalyzed Cross-Coupling with Alkynylzincs and Its Critical Comparison with the Sonogashira Alkynylation
[GRAPHICS]The Pd-catalyzed alkynylation of various alkenyl halides and triflates with alkynylzincs proceeds well even with alkynyl derivatives containing electron-withdrawing groups. The reaction appears to be highly general. Noteworthy is that the corresponding Sonogashira reactions under various reported conditions are significantly less satisfactory in all cases performed in this study.