Making Use of the Functional Group Combination of a Phosphane/Borane Lewis Pair Connected by an Unsaturated Four‐Carbon Bridge

Chen, Guoqiang; Daniliuc, Constantin G.; Kehr, Gerald; Erker, Gerhard

doi:10.1002/ejic.201700570

Cited by 4 publications

(4 citation statements)

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“…4‐(Trimethylsilyl)‐3‐butyn‐2‐one has been used once before in FLP chemistry. With a C 4 ‐bridged B/P‐based Lewis pair, a completely different bicyclic product was isolated, which might be formed through an intramolecular allylboration reaction . Also, in this case, the ethynyl group is not affected.…”

Section: Resultsmentioning

confidence: 93%

Reactions of an Aluminium/Phosphorus Frustrated Lewis Pair (FLP) with α,β‐Unsaturated Carbonyl Compounds: FLPs as Efficient Two‐Electron Reductants with the Formation of Enolates, a cis‐Enediolate, and an Allene

Lange

Tendyck

Wegener

et al. 2018

Chemistry A European J

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The Al/P-based frustrated Lewis pair (FLP) Mes P-C(AltBu) =C(H)Ph (1; Mes=mesityl) reacted as an efficient two-electron reductant with benzil to afford a cis-enediolate that was coordinated to the FLP through P-O and Al-O bonds and the formation of a seven-membered heterocycle (2). The phosphorus atom is oxidised from +III to +V. Similar heterocycles (3 a to 3 f) were formed if 1 was treated with various enones (acrolein, acrylate, acrylamide). The resulting enolates are bound to the FLP through P-C and Al-O bonds. Cyclopropenone gave an adduct (4) with the C=O bond coordinated by P and Al. Ynones gave a fascinating variety of different structures. 1,3-Diphenylprop-2-yn-1-one afforded a remarkable allene-type moiety with two cumulated C=C bonds (5); 3-hexyn-2-one yielded a ligand with two conjugated C=C bonds by C-H bond activation at the carbonyl methyl group (7); and 4-(trimethylsilyl)-3-butyn-2-one reacted by C-H bond cleavage, formation of an enolate group with a terminal C=C bond, and shift of the proton to the P atom (8). The C≡C bond was not affected. Allene compound 5 rearranged at elevated temperature and in daylight through the formation of a tricyclic compound by C-H bond activation and C-C bond formation. DFT calculations on this unusual rearrangement suggest insertion of the central allene C atom into the C-H bond of a methyl group and the intermediate formation of a C ring.

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Section: Resultsmentioning

confidence: 93%

Reactions of an Aluminium/Phosphorus Frustrated Lewis Pair (FLP) with α,β‐Unsaturated Carbonyl Compounds: FLPs as Efficient Two‐Electron Reductants with the Formation of Enolates, a cis‐Enediolate, and an Allene

Lange

Tendyck

Wegener

et al. 2018

Chemistry A European J

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“…In the proton NMR spectrum, the TEMPOH N−H resonance appears at 6.53 ppm. Previous reports of TEMPO protonated at the N−H position include complexes of B, 25 Ni, 26 Zr, 27 and Ir, 28 and those TEMPOH N−H resonances were observed at 7.25, 7.62, 7.36, and 12.32 ppm, respectively. Broad IR absorption bands appear at 3403 and 3255 cm −1 and are reasonably attributed to the N−H bonds in HONO 2− and in TEMPOH, respectively.…”

Section: ■ Introductionmentioning

confidence: 75%

A Ligand Protonation Series in Aluminum(III) Complexes of Tridentate Bis(enol)amine Ligand

2018

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A series of aluminum(III) complexes supported by the tridentate bis(enol)amine ligand (ONO, 1,1′-azanediylbis(3,3-dimethylbutan-2-one)) in two protonation states have been synthesized and characterized structurally. Reaction of AlCl 3 with singly deprotonated H 2 ONO − afforded pseudooctahedral [(H 2 ONO − ) 2 Al][AlCl 4 ] (1). AlCl 3 was also reacted with doubly deprotonated HONO 2− to afford the five-coordinate, pseudotrigonal bipyramidal complex (HONO 2− )AlCl(THF) (2). The reaction of complex 2 with HCl yielded complex 1, which demonstrates reversible protonation of the ligand backbone. Synthesis of an Al(III) complex of ONO 3− was not achieved using a variety of Lewis bases. An attempt to deprotonate complex 2 with t BuOK yielded [(HONO 2− )Al](μ-t BuO) (3), with no change to the ligand protonation state.

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“…Vinyl boranes 197 (R = propyl) also react with TEMPO, Scheme . , First, a Lewis acid–base adduct 198 is formed, and for R = alkyl, HAT to the N-radical cation generates the allyl radical 199 , which recombines with a second equivalent of TEMPO to give product 200 . For dienyl boranes, the nitrogen radical cation of the Lewis acid–base adduct 198 reacts in a 4- exo -cyclization to the allyl radical 201 , which is finally trapped with TEMPO to afford product 202 …”

Section: Oxidation Reactionsmentioning

confidence: 99%

Organic Synthesis Using Nitroxides

Leifert

Studer

2023

Chem. Rev.

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Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R 1 R 2 N−O • . The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R 1 and R 2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R 1 R 2 N�O + ) or reduced to anions (R 1 R 2 N−O − ), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C−O bonds, allowing for the thermal generation of C radicals through reversible C−O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.

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Making Use of the Functional Group Combination of a Phosphane/Borane Lewis Pair Connected by an Unsaturated Four‐Carbon Bridge

Cited by 4 publications

References 58 publications

Reactions of an Aluminium/Phosphorus Frustrated Lewis Pair (FLP) with α,β‐Unsaturated Carbonyl Compounds: FLPs as Efficient Two‐Electron Reductants with the Formation of Enolates, a cis‐Enediolate, and an Allene

Reactions of an Aluminium/Phosphorus Frustrated Lewis Pair (FLP) with α,β‐Unsaturated Carbonyl Compounds: FLPs as Efficient Two‐Electron Reductants with the Formation of Enolates, a cis‐Enediolate, and an Allene

A Ligand Protonation Series in Aluminum(III) Complexes of Tridentate Bis(enol)amine Ligand

Organic Synthesis Using Nitroxides

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