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Biomedical subjects

Ei-ichi Negishi

Publications and source records attributed to Ei-ichi Negishi.

9 recordsLinked to original sources
PubMed2006

Highly efficient and selective synthesis of conjugated triynes and higher oligoynes of biological and materials chemical interest via palladium-catalyzed alkynyl-alkenyl coupling.

Iteration of a Pd-catalyzed reaction of alkynyl- and oligoynylzincs with (E)-ICH=CHCl followed by metalation-termination with electrophiles(E) has provided a linear route to conjugated tri- and tetraynes, and Pd-catalyzed monoalkynylation of 1,1-dibromoenynes accompanied by dehydrobromination has provided a convergent route to conjugated tri- , tetra- , and pentaynes. Both display unprecedented high efficiency and selectivity. [reaction: see text]

Aldehydes↗
PubMed2006

A convenient and genuine equivalent to HZrCp2Cl generated in situ from ZrCp2Cl2-DIBAL-H.

[reaction: see text] Slow addition of 1 equiv of (i)Bu2AlH to ZrCp2Cl2 in THF provides a convenient route to either HZrCp2Cl-(i)Bu2AlCl (Reagent I) or HZrCp2Cl (Reagents II and III). The latter represents a highly convenient route to genuine HZrCp2Cl, while Reagent I is useful for regio- and stereoselective conversion of 1- and 2-alkynes into (E)-1-iodo-1-alkenes and (E)-2-iodo-2-alkenes, respectively.

Alkenes↗
PubMed2006

Catalytic, efficient, and syn-selective construction of deoxypolypropionates and other chiral compounds via Zr-catalyzed asymmetric carboalumination of allyl alcohol.

An efficient, syn-selective, all catalytic asymmetric protocol for the synthesis of alpha,omega-diheterofunctional deoxypolypropionates via Zr-catalyzed asymmetric carboalumination (ZACA reaction) was developed. The success of the method critically hinges on the one-pot conversion of unprotected allyl alcohol into TBS-protected (R)- or (S)-3-iodo-2-methyl-1-propanol (1) of 91% enantiomeric purity in 82% yield via (i) Zr-catalyzed asymmetric methylalumination, (ii) iodination, and (iii) protection with TBSCl. After zincation of 1, its Pd-catalyzed cross-coupling with various organic halides can give various organic derivatives, including 3 and 4, which can serve as key intermediates for efficient and selective syntheses of deoxypolypropionates, such as doliculide and 2,4,6,8-tetramethyldecanoic acid, and other chiral compounds, such as callystatin A. Selective monocarboalumination of 1,4-pentadiene (5 equiv) gave, after oxidation, the expected product 5, but it was 0% ee. A plausible mechanism for racemization has been proposed and experimentally supported.

Albumins↗
PubMed2005

A quarter of a century of explorations in organozirconium chemistry.

Systematic explorations of organozirconium chemistry over the past quarter of a century have led to the discoveries and development as well as structural and mechanistic clarifications of novel Zr-catalyzed and -promoted carbon-carbon bond-forming reactions including (i) Ni- or Pd-catalyzed cross-coupling reaction of organozirconiums, (ii) Zr-catalyzed carboalumination of alkynes, (iii) Zr-catalyzed asymmetric carboalumination of alkenes, (iv) generation and carbometallative ring expansion of zirconacyclopropanes and zirconacyclopropenes and a myriad of their transformations and (v) various organozirconium migratory insertion reactions.

History, 20th Century↗
PubMed2004

Efficient and selective synthesis of 6,7-Dehydrostipiamide via Zr-catalyzed asymmetric carboalumination and Pd-catalyzed cross-coupling of organozincs.

[structure: see text] 6,7-Dehydrostipiamide has been synthesized in 23% yield in 15 steps in the longest linear sequence through the application of the Zr-catalyzed asymmetric carboalumination and the Pd-catalyzed organozinc cross-coupling in addition to the Brown crotylboration, the Corey-Peterson olefination, and the Corey-Fuchs reaction for carbon-carbon bond formation.

Catalysis↗
PubMed2004

Use of InCl(3) as a cocatalyst and a Cl(2)Pd(DPEphos)-P(2-furyl)(3) catalyst system for one-pot hydrometalation-cross-coupling and carbometalation-cross-coupling tandem processes.

One-pot conversion of alkynes to regio- and stereodefined alkenylmetals containing Al and Zr via hydrometalation or carbometalation followed by their Pd-catalyzed cross-coupling with (E)-ICH=CHBr or (E)-ICH=CHCl proceeds cleanly and selectively to give the corresponding 1-halo-1,3-dienes in excellent yields using a catalyst system consisting of Cl(2)Pd(DPEphos), DIBAL-H, and TFP (catalyst A) with InCl(3) as a cocatalyst.

Alkynes↗
PubMed2003

Clean inversion of configuration in the Pd-catalyzed cross-coupling of 2-bromo-1,3-dienes.

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.

Alkenes↗
PubMed2002

A novel, highly selective, and general methodology for the synthesis of 1,5-diene-containing oligoisoprenoids of all possible geometrical combinations exemplified by an iterative and convergent synthesis of coenzyme Q(10).

[reaction: see text] A truly general, versatile, and highly regio- and stereoselective methodology for the synthesis of terpenoids containing 1,5-diene units of E and/or Z geometry critically involves Pd-catalyzed homoallyl- and homopropargyl-alkenyl coupling and Zr-catalyzed carboalumination of alkynes. By using this methodology, coenzyme Q(10), (E,Z,E)-geranylgeranoil, and other natural or unnatural compounds have been synthesized efficiently.

Alkynes↗