Substituierte 2,5‐Dihydro‐1,2,5‐oxoniadiboratole, <i>cis</i>‐1,2‐Diborylalkene und 1,2,5‐Oxadiborolane – Herstellung und Charakterisierung

Köster, Roland; Seidel, Günter

doi:10.1002/cber.19921250608

Cited by 4 publications

(1 citation statement)

References 21 publications

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“…To better understand this 1:2 10h /OH -1 stoichiometry, we carried out the hydrolysis of [9-BBN-H] 2 in THF (25 °C, 3 h) with 1.0 equiv of NaOH(aq). By 11 B NMR, the intermediate HO-9-BBN ( 16 δ 56.3) or O(9-BBN) 2 (δ 57.5) at δ 54.5 was observed to ultimately produce mainly its hydroxy complex, [(HO) 2 -9-BBN] -1 ( 17 11 B NMR δ 9.6) which, when fully formed, exhibits a signal at δ 4 (Scheme ) …”

Section: Resultsmentioning

confidence: 99%

Alkylboranes in the Suzuki−Miyaura Coupling: Stereochemical and Mechanistic Studies

1998

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Both erythro and threo isomers of B-(3,3-dimethyl-1,2-dideuterio-1-butyl)-9-BBN (6) were prepared from 3,3-dimethyl-1-butyne (4) through a hydroboration-deuteronolysis-hydroboration sequence employing first 9-BBN-H and then 9-BBN-D, or in reverse order, respectively. Employing the Whitesides protocol, the stereochemistry of B --> Pd alkyl group transfer in the Suzuki-Miyaura coupling of 6 to PhBr has been found to occur with complete retention of configuration with respect to carbon. For the coupling process, the Lewis acidity of the boron plays an important role with B-alkyl-9-BBN (10) forming [HO(R)-9-BBN](-)(1) (12) with the added base, in marked contrast to their B-alkyl-9-oxa-10-borabicyclo[3.3.2]decane counterparts (R-OBBD, 11) which do not. This behavior parallels their coupling rates with the exclusive reaction of 10 over 11 in competitive experiments. Five five possible roles were demonstrated for the added base in the coupling: (1) the formation of 12, (2) the hydrolysis of Ph(Ph(3)P)(2)PdBr (14) to provide monomeric Ph(Ph(3)P)(2)PdOH (15), (3) the complexation of HOBR(2) byproducts which can compete with 10 for base, (4) accelerated coupling rates for 11, and (5) catalyst regeneration. Kinetic studies reveal that the couplings are zero-order in the borane but for 10 exhibit a first-order dependence on [PhBr] (i.e., oxidative addition), while for 11 exhibit a first-order dependence on [OH(-)(1)] (i.e., Pd(II)X hydrolysis). These data are interpreted in terms of attack of 14 by 12 to form a hydroxo &mgr;(2)-bridged intermediate 8(a) [PhL(2) Pd <-- (OH)BR(9-BBN)]. This provides the precursor to transmetalation through a four-centered transition state 9. Because the analogous hydroxyborate complex is absent for 11, 14 is hydrolyzed by OH(-)(1) forming 15 in a slower process, with this ultimately reacting with 11 to form a related intermediate 8(b) [PhL(2) Pd(OH) --> BR(OBBD)] which also collapses to products through 9.

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Section: Resultsmentioning

confidence: 99%

Alkylboranes in the Suzuki−Miyaura Coupling: Stereochemical and Mechanistic Studies

1998

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Ethyl‐substituierte 2,5‐Dihydro‐1,2,5‐oxadiborole

1994

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Ethyl-substituted 2,5-Dihydro-1 ,2,5-oxadiboro1esl1~Four N-Lewis base-(1,2,5-oxadiboroles) rac-5(Do) [Do = ammonia (NH,), quinuclidine (a), pyridine (Py), y-picoline (yPic)] of k(Et)OB(Et)C(Et)=e(Et) (5, identical with 11) are prepared by reaction of cis-EtzBC(Et)=C(Et)BEt2 (A) with KNHz via the tetraethyl-substituted (m) heterocycles 1-4. k(Et)N(SiMe,)B(Et)C(Et)=C(Et) (4) reacts with water with elimination of Me,SiOH to give rac-5(NH3). The latter undergoes exchange reactions with various N-bases (Py, yPic, Q) quantitatively forming the 1: 1 addition compounds racS(Do) [Do = yPic (X-ray structure analysis)]. rac-5(NH3) reacts with Ph3B to yield H3N-BPh3 and the unstable compound 5, which dimerises t' o (5)* and/or reacts with (EtBO) elimination to afford the boroxin (EtBO), and, presumably,to EtPbMe, and presumably 5 or to the rearranged heterocycle k(Et)OB(Et)C(Et,)k(Et, PbMe,) (?).Tetraorgano-substituierte 2,5-Dihydro-1,2,5-0xadiborole sind cyclische Vinyldiboroxane, deren Verwendung als Reagenzien zur 1,2-Vinyloborierung von Carbonyl-Verbindungen und als q4-(2e-Fiinfring)-Liganden von Ubergangsmetallfragmenten interessant ist. Wir wollten feststellen, ob und wie (-)-Heterocyclen hergestellt und die aufgrund von Literat~rangaben".~] vermutlich instabilen Fiinfringe in situ aus geeigneten Depotverbindungen freigesetzt werden konnen. 2,s-Dihydro-1,2,5-thiadiborole sind demgegeniiber stabile Verbindungen[2bl. 2,5-Dihydro-l,2,5-oxadiborole mit weiteren elektronenspendenden Substituenten wie z.B. rnit exocyclischen OR-oder NR2-Resten an den Roratomen haben wir nicht untersucht, da derartige Verbindungen eine vergleichsweise geringe Reaktivitat haben durften.Uber Lewisbase-freie 2,5-Dihydro-l,2,5-oxadiborole ist nur vorlaufig berichtet worden, so uber das 2,5-Dichlor-3,4dimethyl-Derivat I[2] sowie die all-Ethyl-Verbindung IIL3]. Da wegen fehlender zusatzlicher Verlautbarungen die ( m ) -C y c l e n ohne Komplexpartner offensichtlich instabil sind, haben wir zunachst versucht, Lewisbase-Addukte der Organo-substituierten 2,5-Dihydro-1,2,5-oxadiborole praparativ zu gewinnen. Wir berichten hier uber Synthesewege zu der perethylierten Verbindung I1 (im folgenden rnit 5 bezeichnet) aus 3,4-Bis(diethylboryl)-cis-3-hexen (A)[4,51 und aus dem Kaliumsalz B, das aus A rnit Kaliumhydroxid nach G1. (a) leicht zuganglich id6].

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ChemInform Abstract: Boron Compounds. Part 105. Substituted 2,5‐Dihydro‐1,2,5‐ oxoniadiboratoles, cis‐1,2‐Diborylalkenes, and 1,2,5‐Oxadiborolanes ‐ Preparation and Characterization.

Koêster

Seidel

1992

ChemInform

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Substituierte 2,5‐Dihydro‐1,2,5‐oxoniadiboratole, cis‐1,2‐Diborylalkene und 1,2,5‐Oxadiborolane – Herstellung und Charakterisierung

Cited by 4 publications

References 21 publications

Alkylboranes in the Suzuki−Miyaura Coupling: Stereochemical and Mechanistic Studies

Alkylboranes in the Suzuki−Miyaura Coupling: Stereochemical and Mechanistic Studies

Ethyl‐substituierte 2,5‐Dihydro‐1,2,5‐oxadiborole

ChemInform Abstract: Boron Compounds. Part 105. Substituted 2,5‐Dihydro‐1,2,5‐ oxoniadiboratoles, cis‐1,2‐Diborylalkenes, and 1,2,5‐Oxadiborolanes ‐ Preparation and Characterization.

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