Abstract
Deep eutectic solvents (DESs) have been used for the first time as a sustainable medium in radical-mediated molecular organic synthetic protocols. This study reports an efficient protocol for the C–C bond formation through radical conjugate addition of simple olefins (di- and trisubstituted). An inexpensive and abundant iron catalyst [Fe(acac)3] together with nontoxic silane (poly(methylhydrosiloxane) (PMHS)) was employed, using choline chloride/ethylene glycol (1:2) as a solvent under air and mild reaction conditions. Different functional groups were well tolerated, and also, the reaction could be carried out on a gram scale with excellent yields.
Highlights
Deep eutectic solvents (DESs) have been applied in several organic transformations, the field of radical-mediated organic reactions remains unexplored, with only a few examples related to polymer material synthesis.[67−72] we have developed an unprecedented, practical, and sustainable methodology for the multicomponent reductive coupling of a broad range of olefins via radicals, which utilizes (i) a readily available and inexpensive iron catalyst, (ii) poly(methylhydrosiloxane) (PMHS), a cheap, nontoxic, and air- and moisture-stable silane as an effective reducing agent,[73] and (iii) DESs as a sustainable reaction medium
Our initial investigations started by optimizing the reaction conditions, using 1-methylcyclohexene (1a) and methyl acrylate (2a) as a model reaction (Table 1)
The highly tunable properties of DESs led to the development of an efficient and sustainable methodology for C−C bond formation through an iron-catalyzed radical alkene crosscoupling reaction
Summary
Radical reactions have gained widespread application for the construction of C−C bonds, mainly through the conjugate addition of carbon-centered radicals into unsaturated electrophiles.[1−5] The development of new methodologies devoted to creating C−C bonds in an efficient and sustainable manner would be desirable in the area of green chemistry since it allows the generation of complex molecules of interest as agrochemicals, pharmaceuticals, and polymers.[6]. Among the plethora of carbon radical precursors, olefins represent ideal starting materials since they can be found in a variety of feedstock chemicals and in complex natural compounds, and compared to other radical precursors, are typically bench-stable Having this in mind, the application of hydrogen-atom transfer (HAT) to generate carbon-centered radicals from olefins is considered a robust strategy to develop new bondforming reactions in organic synthesis (Scheme 1).[7]. There are supposed to exist more than one million possible mixtures, affording the possibility of designing a solvent for each different application Due to their high versatility, tunability, and sustainability, their use as a medium to carry out metalcatalyzed organic transformations has attracted the interest of organic chemists over the last years.[64−66] the change of a typical organic solvent by a DES in a reaction is challenging per se due to the high density of hydrogen bonds. DESs have been applied in several organic transformations, the field of radical-mediated organic reactions remains unexplored, with only a few examples related to polymer material synthesis.[67−72] we have developed an unprecedented, practical, and sustainable methodology for the multicomponent reductive coupling of a broad range of olefins (including 1,2-disubstituted ones) via radicals, which utilizes (i) a readily available and inexpensive iron catalyst, (ii) poly(methylhydrosiloxane) (PMHS), a cheap, nontoxic, and air- and moisture-stable silane as an effective reducing agent,[73] and (iii) DESs as a sustainable reaction medium
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