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Highly(?98%) Selective Trisubstituted Alkene Synthesis of Wide Applicability via Fluoride-Promoted Pd-Catalyzed Cross-Coupling of Alkenylboranes.

ABSTRACT: (Z)-?-bromo-1-propenyl(pinacol)borane(4), recently made available in 85% yield as a ?98% isomerically pure compound via bromoboration of 1-propyne, has been converted to ?-alkyl-, aryl-, and alkenyl-substituted (Z)-2-methyl-1-alkenyl(pinacol)boranes(2a) in ca. 75% yield based on propyne via Pd-catalyzed Negishi alkenylation with suitable organozinc bromide. The previously sluggish and modest-yielding Suzuki alkenylation of ?,?-disubstituted alkenylboranes has been significantly promoted by fluorides, especially nBu4NF(TBAF) or CsF to give trisubstituted alkenes, i.e., (Z)-?-Me-substituted 3-i-3-xi and (E)-?-Ph-substituted 2b-i and 2b-ii. In all cases, each alkene product was formed in a ?98% seteoselectivity. The propyne-based protocol nicely complements the widely used Zr-catalyzed alkyne methylalumination-Pd-catalyzed alkenylation by providing a highly stereoselective(?98%) route to (Z)-Me-substituted alkenes.

SUBMITTER: Negishi EI 

PROVIDER: S-EPMC3747006 | biostudies-literature | 2010 Dec

REPOSITORIES: biostudies-literature

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Highly(≥98%) Selective Trisubstituted Alkene Synthesis of Wide Applicability via Fluoride-Promoted Pd-Catalyzed Cross-Coupling of Alkenylboranes.

Negishi Ei-Ichi EI   Tobrman Tomas T   Rao Honghua H   Xu Shiqing S   Lee Ching-Tien CT  

Israel journal of chemistry 20101201 5-6

(<i>Z</i>)-<i>β</i>-bromo-1-propenyl(pinacol)borane(<b>4</b>), recently made available in 85% yield as a ≥98% isomerically pure compound via bromoboration of 1-propyne, has been converted to <i>β-</i>alkyl-, aryl-, and alkenyl-substituted (<i>Z</i>)-2-methyl-1-alkenyl(pinacol)boranes(<b>2a</b>) in ca. 75% yield based on propyne via Pd-catalyzed Negishi alkenylation with suitable organozinc bromide. The previously sluggish and modest-yielding Suzuki alkenylation of <i>β</i>,<i>β</i>-disubstituted  ...[more]

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