Copper(I)-Catalyzed Formal Carboboration of Alkynes: Synthesis of Tri- and Tetrasubstituted Vinylboronates
摘要:
The first copper-catalyzed formal carboboration of alkynes, in which a C-B bond and a C-C bond are created in a single catalytic cycle, is presented. The reaction proceeds with high regioselectivity and syn-stereoselectivity to form tri- and tetrasubstituted vinylboronic esters from commercially available bis-(pinacolato)diboron. A subsequent cross-coupling reaction gives access to highly substituted alkenes.
The Synthesis of Internal Conjugated (<i>E</i>)-Enynyldialkylboranes and Their Applications to the Syntheses of Conjugated Alkynones, Conjugated (<i>E</i>)-Enynes, and Conjugated Enynes Bearing an Unsaturated Group on the Double Bond
作者:Masayuki Hoshi、Yuzuru Masuda、Akira Arase
DOI:10.1246/bcsj.58.1683
日期:1985.6
(E)-Enynyldialkylboranes, thus obtained, gave regio- and/or stereospecifically defined corresponding conjugated alkynones by alkaline hydrogen peroxide oxidation, conjugated (E)-enynes by protonolysis with acetic acid, and conjugated enynes bearing an unsaturated group on the internal alkenyl carbon atom by bis(acetylacetonato)copper-catalyzed cross-coupling reaction with allyl bromide or 1-bromo-1-hexyne respectively
Preparation of polyfunctional diorganomercurials and their transmetallation to diorganozincs. Applications to the preparation of optically active secon
作者:Michael J. Rozema、Duddu Rajagopal、Charles E. Tucker、Paul Knochel
DOI:10.1016/0022-328x(92)88002-z
日期:1992.10
Two new methods of preparation of functionalized diorganomercurials have been developed. The first method involves a substitution reaction of (ICH2)2Hg with zinc-copper reagents FG-RCu(CN)ZnI in THF/DMF at - 60-degrees-C. Functional groups such as an ester, nitrile, ketone, phosphonate, halide, and boronic ester are tolerated in this reaction. The second method involves a reductive transmetallation between polyfunctional organozinc halides and mercurous chloride (Hg2Cl2). This very convenient procedure provides a rapid route to various functionalized diorganomercurials in good yields (61-89% yield). The synthetic utility of these mercury organometallics is demonstrated. Their transmetallation with zinc dust (toluene, 80-degrees-C, 3-5 h) affords dialkylzincs which add enantioselectively to aldehydes in the presence of a catalytic amount (20 mol%) of the norephedrine derivative 13. This transmetallation can also be used to prepare stereoselectively (E)-alkenylzinc halides (> 98% E). Addition of Cl(H)ZrCp2 to (E)-5-chloropentenylzinc bromide in CH2Cl2 (25-degrees-C, 1 min) affords a 1,1-bimetallic of zinc and zirconium Cl(CH2)4CH(ZnBr)ZrCp2(Cl) which reacts stereoselectively with an aldehyde providing the (E)-disubstituted olefin (49% yield; 100% E).