New Advances in Titanium-Mediated Free Radical Reactions

Rossi, Bianca; Prosperini, Simona; Pastori, Nadia; Clerici, Angelo; Punta, Carlo

doi:10.3390/molecules171214700

Cited by 51 publications

(22 citation statements)

References 175 publications

(167 reference statements)

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“…The intermolecular radical addition to activated imines using a TiCl 3 /ArN 2 + system was first reported by Clerici and Porta [65] in 1990 and has been reviewed by Pastori et al [59] in 2009 and by Punta and co-workers in 2012 [66]. Here, a primary aromatic amine, an aldehyde and an arenediazonium salt were converted to a secondary amine in a three-component reaction (Scheme 22).…”

Section: Addition To Aliphatic Iminium Ionsmentioning

confidence: 99%

“…HCl) reaction conditions. The resulting amine radical cation is further reduced to the amine by another equivalent of Ti 3+ (Scheme 23) [66]. Hence, Ti 3+ acts as a radical initiator as well as a radical terminator in the final reduction [67].…”

Section: Addition To Aliphatic Iminium Ionsmentioning

confidence: 99%

“…Further investigations allowed to extend the scope of the reaction to the addition of different nucleophilic radicals to the C=N bond so that e.g. hydroxymethylation or carbamoylation of aldimines or ketimines became feasible (Scheme 27) [66,74,75,76,77,78].…”

Section: Addition To Aliphatic Iminium Ionsmentioning

confidence: 99%

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Radical Addition to Iminium Ions and Cationic Heterocycles

2014

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Carbon-centered radicals represent highly useful reactive intermediates in organic synthesis. Their nucleophilic character is reflected by fast additions to electron deficient C=X double bonds as present in iminium ions or cationic heterocycles. This review covers diverse reactions of preformed or in situ-generated cationic substrates with various types of C-radicals, including alkyl, alkoxyalkyl, trifluoromethyl, aryl, acyl, carbamoyl, and alkoxycarbonyl species. Despite its high reactivity, the strong interaction of the radical's SOMO with the LUMO of the cation frequently results in a high regioselectivity. Intra-and intermolecular processes such as the Minisci reaction, the Porta reaction, and the Knabe rearrangement will be discussed along with transition metal and photoredox catalysis or electrochemical methods to generate the odd-electron species.

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Section: Addition To Aliphatic Iminium Ionsmentioning

confidence: 99%

Section: Addition To Aliphatic Iminium Ionsmentioning

confidence: 99%

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Radical Addition to Iminium Ions and Cationic Heterocycles

2014

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“…The higher molecular weight obtained with Ti(IV) might result from its ability to act as a free radical initiator, thus favouring branching and increasing chain length but eventually leading to gelation. [39,40] Polycondensation reactions using an enzymatically-catalysed transesterification reaction in organic media can be performed at low temperature and avoid metal salts catalysts. This could prevent previously unwanted side reactions to occur.…”

Section: Synthesis Of Polyesters Of Furandiyl Diacrylic Esters (Pfae)mentioning

confidence: 99%

Work‐hardening Photopolymer from Renewable Photoactive 3,3’‐(2,5‐Furandiyl)bisacrylic Acid

et al. 2020

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The design of a photopolymer around a renewable furan‐derived chromophore is presented herein. An optimised semi‐continuous oxidation method using MnO2 affords 2,5‐diformylfuran from 5‐(hydroxymethyl)furfural in gram quantities, allowing the subsequent synthesis of 3,3’‐(2,5‐furandiyl)bisacrylic acid in good yield and excellent stereoselectivity. The photoactivity of the diester of this monomer is confirmed by reaction under UV irradiation, and the proposed [2+2] cycloaddition mechanism supported further by TD‐DFT calculations. Oligoesters of the photoreactive furan diacid with various aliphatic diols are prepared via chemo‐ and enzyme‐catalysed polycondensation. The latter enzyme‐catalysed (Candida antarctica lipase B) method results in the highest Mn (3.6 kDa), suggesting milder conditions employed with this protocol minimised unwanted side reactions, including untimely [2+2] cycloadditions, whilst preserving the monomer's photoactivity and stereoisomerism. The photoreactive polyester is solvent cast into a film where subsequent initiator‐free UV curing leads to an impressive increase in the material stiffness, with work‐hardening characteristics observed during tensile strength testing.

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“…During the course of our ongoing investigation of the role of titanium salts in mediating selective radical transformations [ 13 – 14 ], we have developed new, simple protocols for the synthesis of complex organic compounds through nucleophilic radical addition to imines generated in situ [ 15 ]. Several recent contributions to the field clearly illustrate how the free-radical approach can be considered a valuable alternative to classical ionic protocols [ 16 – 23 ].…”

Section: Introductionmentioning

confidence: 99%

Multicomponent versus domino reactions: One-pot free-radical synthesis of β-amino-ethers and β-amino-alcohols

Rossi¹,

Pastori

Prosperini³

et al. 2015

Beilstein J. Org. Chem.

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SummaryFollowing an optimized multicomponent procedure, an aryl amine, a ketone, and a cyclic ether or an alcohol molecule are assembled in a one-pot synthesis by nucleophilic radical addition of ketyl radicals to ketimines generated in situ. The reaction occurs under mild conditions by mediation of the TiCl4/Zn/t-BuOOH system, leading to the formation of quaternary β-amino-ethers and -alcohols. The new reaction conditions guarantee good selectivity by preventing the formation of secondary products. The secondary products are possibly derived from a competitive domino reaction, which involves further oxidation of the ketyl radicals.

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New Advances in Titanium-Mediated Free Radical Reactions

Cited by 51 publications

References 175 publications

Radical Addition to Iminium Ions and Cationic Heterocycles

Radical Addition to Iminium Ions and Cationic Heterocycles

Work‐hardening Photopolymer from Renewable Photoactive 3,3’‐(2,5‐Furandiyl)bisacrylic Acid

Multicomponent versus domino reactions: One-pot free-radical synthesis of β-amino-ethers and β-amino-alcohols

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