Electrophilic Additions to Double Bonds

Kočovský, Pavel

doi:10.1002/0470857234.ch19

Cited by 5 publications

(1 citation statement)

References 416 publications

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“…Similar stereochemical and mechanistic issues arise in the electrophilic 1, 2-additions of hydrogen halides to olefins and epoxides. Syn additions to CC double bonds are frequently observed at low temperatures with tetrasubstituted olefins, , and increased HX concentration favors the anti mode of addition. However, in contrast to the tendency toward enhanced anti stereoselectivity of the chloro-Prins cyclizations in the nonpolar hydrocarbon solvents noted above, less polar solvents favor syn addition to olefins 22b.…”

Section: Discussionmentioning

confidence: 99%

Syn- and Anti-Selective Prins Cyclizations of δ,ε-Unsaturated Ketones to 1,3-Halohydrins with Lewis Acids

2006

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Ten acyclic and monocyclic delta,epsilon-unsaturated ketones, with and without methyl substituents on the double bond, underwent halide-terminated Prins (halo-Prins) cyclizations under anhydrous conditions in the presence of Lewis acids. TiCl4, TiBr4, BCl3, and BBr3 promoted syn-selective cyclizations to sterically congested chloro- and bromohydrins, while SnCl4, SnBr4, InCl3, ZrCl4, and several other Lewis acids effected highly anti-selective reactions to furnish the corresponding trans halohydrins. The stronger Lewis acids (TiX4 and BX3) favor the syn process that involves axial delivery of a halide ligand. Competition experiments showed that substitution at the delta carbon (methallyl enones) led to increased rates (40-50-fold), while substitution at the epsilon position (cis and trans crotyl enones) retarded the rate and eroded the selectivity of the cyclizations. The trends in syn vs anti selectivity, reactivity, and effects of different Lewis acidic metal halides are rationalized by competitive reaction pathways proceeding through syn carbocation-halide ion pairs and a higher order transition state that leads to inversion of configuration and formation of trans halohydrins, along with cyclic olefins arising from proton elimination.

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Section: Discussionmentioning

confidence: 99%

Syn- and Anti-Selective Prins Cyclizations of δ,ε-Unsaturated Ketones to 1,3-Halohydrins with Lewis Acids

2006

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Efficient E‐Selective Transfer Semihydrogenation of Alkynes by Means of Ligand‐Metal Cooperating Ruthenium Catalyst

et al. 2015

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The manuscript describes an efficient protocol for the E‐selective transfer semihydrogenation of internal alkynes employing a previously described bifunctional ruthenium‐based PC(sp3)P complex, 20 mol% of sodium formate and nearly stoichiometric formic acid. Semihydrogenation of the terminal alkynes results in the formation of the corresponding styrenes. The mechanism of the reaction includes stepwise transfer of both the hydride and the proton of the formic acid to the substrate. This fact allowed for the development of a facile protocol for the synthesis of monodeuterated alkenes by simply applying formic acid/sodium formate/D2O mixture as a hydrogen source. High yields, selectivity and functional group compatibility have been generally achieved.magnified image

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Stereoselective Palladium‐Catalyzed Functionalization of Homoallylic Alcohols: A Convenient Synthesis of Di‐ and Trisubstituted Isoxazolidines and β‐Amino‐δ‐Hydroxy Esters

Malkov

Barłóg

Miller‐Potucka

et al. 2012

Chemistry A European J

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Enantiopure, Boc-protected alkoxyamines 12 and 13, derived from the readily available homoallylic alcohols 4 via a reaction that involves either inversion or retention of configuration, undergo a diastereoselective Pd-catalyzed ring-closing carbonylative amidation to produce isoxazolidines 16/17 (≤50:1 diastereoisomer ratio (d.r.)) that can be readily converted into the N-Boc-protected esters of β-amino-δ-hydroxy acids and their γ-substituted homologues 37. The key carbonylative cyclization proceeds through an unusual syn addition of the palladium and the nitrogen nucleophile across the C=C bond (19→21), as revealed by the reaction of 15, which afforded isoxazolidine 18 with high diastereoselectivity.

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Electrophilic Additions to Double Bonds

Cited by 5 publications

References 416 publications

Syn- and Anti-Selective Prins Cyclizations of δ,ε-Unsaturated Ketones to 1,3-Halohydrins with Lewis Acids

Syn- and Anti-Selective Prins Cyclizations of δ,ε-Unsaturated Ketones to 1,3-Halohydrins with Lewis Acids

Efficient E‐Selective Transfer Semihydrogenation of Alkynes by Means of Ligand‐Metal Cooperating Ruthenium Catalyst

Stereoselective Palladium‐Catalyzed Functionalization of Homoallylic Alcohols: A Convenient Synthesis of Di‐ and Trisubstituted Isoxazolidines and β‐Amino‐δ‐Hydroxy Esters

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