154230-29-2Relevant academic research and scientific papers
ASYMMETRIC ADDITION REACTIONS
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Paragraph 00142, (2016/12/26)
Processes of forming Csp2-Csp3 bonds at the allylic carbon of a cyclic allylic compound starting material are disclosed, in which a racemic mixture of a cyclic allylic compound having a leaving group attached to the allylic carbon is reacted with a compound having a nucleophilic carbon atom in the presence of a Rh(l), Pd(ll) or Cu(l) pre-catalyst and a chiral ligand. The reaction products containing the newly-formed Csp2-Csp3 bond are generated in high stereoisomeric excess, and may therefore serve as important organic building blocks in the preparation of new agrochemicals and pharmaceuticals.
N-B dative bond-induced [3.3.0] bicyclic boronate-tethered exo-selective intramolecular Diels-Alder reaction
Feng, Chao,Wang, Hong,Xu, Liang,Li, Pengfei
supporting information, p. 7136 - 7139 (2015/07/01)
We report herein a highly exo-selective intramolecular Diels-Alder reaction of alkenyl boronates which employs an N-B dative bond-involved bicyclic rigid tether. Complex C(sp3)-rich polycyclic molecules containing up to 8 stereocenters can be readily formed via an operationally simple two-step procedure.
Anomalies in the stereoselectivity of the petasis reaction using styrenyl boronic acids
Churches, Quentin I.,Johnson, James K.,Fifer, Nathan L.,Hutton, Craig A.
scheme or table, p. 62 - 67 (2011/10/05)
The Petasis three-component coupling reaction of N-benzylphenylglycinol, glyoxylic acid, and styrenylboronic acids allows for the efficient synthesis of functionalized homoarylalanine derivatives. The reactions were shown to proceed in high yield but low selectivity, regardless of the nature of the substituent on the styrenylboronic acid component. Anomalies in the stereoselectivity of these reactions compared with previously reported results have been traced to the source of the organoboronic acid. Asymmetric dihydroxylation of the unsaturated amino acid derivatives enables a highly efficient route to dihydroxyhomoarylalanine derivatives. CSIRO 2011.
Vinylborane formation in rhodium-catalyzed hydroboration of vinylarenes. Mechanism versus borane structure and relationship to silation
Brown, John M.,Lloyd-Jones, Guy C.
, p. 866 - 878 (2007/10/02)
Attempted catalytic hydroboration of (4-methoxyphenyl)ethene 1 with R,R-3-isopropyl-4-methyl-5-phenyl-1,3,2-oxazaborolidine 6 proceeded extremely slowly relative to the 3-methyl analog 2 derived from φ-ephedrine when diphosphinerhodium complexes were employed. With phosphine-free rhodium catalysts, especially the 4-methoxy-phenylethene complex 7, the reaction proceeded rapidly and quantitatively to give only the corresponding (E)-vinylborane 9 and 4-methoxyethylbenzene 8 in equimolar amounts. Isotopic labeling and kinetic studies demonstrated that this reaction pathway is initiated by the formation of a rhodium hydride with subsequent reversible and regiospecific H-transfer to the terminal carbon, giving an intermediate which adds the borane and then eliminates the hydrocarbon product. Further migration of the secondary borane fragment from rhodium to the β-carbon of the coordinated olefin occurs, followed by Rh-H β-elimination which produces the vinylborane product and regenerates the initial catalytic species. When the same catalytic reaction is carried out employing catecholborane in place of the oxazaborolidine, an exceedingly rapid turnover occurs. The products are again 4-methoxyethylbenzene and the (E)-vinylborane 23 but accompanied by the primary borane 24 in proportions which vary with the experimental conditions. None of the secondary borane, which is the exclusive product when pure ClRh(PPh3)3 is employed as catalyst, is formed. The product variation as a function of initial reactant concentration was fitted to a model in which the rhodium-borane intermediate in the catalytic cycle undergoes two competing reactions-β-elimination of Rh-H versus addition of a further molecule of catecholborane. The model demonstrates that a kinetic isotope effect of 3.4 operates in the β-elimination step, but none is evident in the addition of catecholborane B-D to rhodium. A similar analysis was successfully applied to the catalytic hydrosilylation of 4-methoxystyrene, with HSiEt3, again employing the phosphine-free rhodium catalyst 7; the product distribution between primary silane 29 and vinylsilane 28 was successfully predicted. The results intimate that silation (i.e., the formation of vinylsilanes under the conditions of catalytic hydrosilylation) can best be explained by a Rh-H based mechanistic model rather than the commonly assumed variant on the Chalk-Harrod catalytic cycle. They provide an explanation for the "oxygen effect" on the rate of Rh-catalyzed hydrosilylations.
