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D. Cassú, T. Parella, M. Solà, A. Pla-Quintana and A. Roglans
Chem. Eur. J., 23, 14889-14899 (2017). DOI
Rhodium-catalysed [2+2+2] cycloaddition reactions of linear allene-ene-ynes to afford fused tricyclic scaffolds. Insights into the mechanism.
Allene‐(E)‐ene‐yne N‐tosyl‐tethered substrates 3 a–3 h were efficiently prepared and their rhodium‐catalyzed [2+2+2] cycloaddition reactions were evaluated. The cycloadditions are chemoselective as only the proximal double bond of the allene reacted to afford exocyclic double bonds in the fused‐tricyclic scaffolds. The stereoselectivity depended on the catalytic system used. Reactivity between allene, alkene, and alkyne was studied for the first time by density functional theory calculations. This mechanistic study determines the order in which the unsaturated groups take part in the catalytic cycle.
E. Haraburda, M. Fernández, A. Gifreu, J. Garcia, T. Parella, A. Pla-Quintana and A. Roglans
Adv. Synth. Cat., 359, 506-512 (2017).DOI
Chiral Induction in Intramolecular Rhodium-Catalyzed [2+2+2] Cycloadditions of Optically Active Allene–ene/yne–allene Substrates
Allene‐yne‐allene and allene‐ene‐allene N‐tosyl‐linked substrates with two chiral centres in the α‐position of the allene moiety were satisfactorily prepared starting both from racemic and chiral propargylic alcohols. The Wilkinson's complex‐catalyzed [2+2+2] cycloaddition reaction of these substrates was evaluated. In the case of enantiomerically pure bisallenes, high stereoselectivity was observed, giving a diastereomerically pure cycloadduct. The chirality of starting bisallene substrates can be completely transferred to the cycloadducts, representing an atom‐economical and enantiospecific process for the construction of fused polycycles. However, when reacting an oxygen‐linked allene‐ene‐allene substrate, the stereoselectivity decreased and two diastereoisomers were formed. A detailed characterization study of the resulting cycloadducts allowed us to identify the enantioisomer generated in the cycloaddition.
M. Fernández, M. Parera, T, Parella, A. Lledó, J, Le Bras, J, Muzart, A, Pla-Quintana and A, Roglans
Adv. Synth. Cat., 358, 1848-1853 (2016). DOI
Rhodium-Catalyzed [2+2+2] Cycloadditions of Diynes with Morita–Baylis–Hillman Adducts: A Stereoselective Entry to Densely Functionalized Cyclohexadiene Scaffolds
A rhodium-catalyzed asymmetric synthesis of 5,5-disubstituted cyclohexa-1,3-dienes has been achieved by [2+2+2] cycloaddition reactions between diynes and Morita–Baylis–Hillman (M-BH) adducts as unsaturated substrates. Products containing two adjacent chiral centres (quaternary and tertiary, respectively) were obtained with complete diastereoselectivity and high enantioselectivity (84– 97%) through a kinetic resolution of the M-B-H adduct. Furthermore, these highly substituted cyclohexadienes reacted with dienophiles to afford the corresponding Diels–Alder cycloadducts in good yields.
O. Torres, T. Parella, M. Solà, A. Roglans and A. Pla-Quintana
Chem. Eur. J., 21, 16240-16245 (2015). DOI
Enantioselective Rhodium(I) Donor Carbenoid-Mediated Cascade Triggered by a Base-Free Decomposition of Arylsulfonyl Hydrazones
The reaction of diyne arylsulfonyl hydrazone substrates under rhodium(I)/BINAP catalysis gives access to sulfonated azacyclic frameworks in a highly enantioselective manner. This new cascade process considerably increases the molecular complexity by generating two C¢C bonds, one C¢S bond, and one C¢H bond. Theoretical calculations, competitive experiments, and deuterium labeling have jointly been used to propose a mechanism that accounts for the reaction. The mechanism involves the formation of vinyl rhodium carbenoids, hydride migratory insertion, and intermolecular stereoselective nucleophilic attack. The last two steps are the key to the stereoselectivity of the process.
M. Fernández, M. Ferré, A. Pla-Quintana, T. Parella, R. Pleixats, and A. Roglans
Eur. J. Org. Chem., 28, 6242-6251 (2014). DOI
Rhodium-NHC Hybrid Silica Materials as Recyclable Catalysts for [2+2+2] Cycloaddition Reactions of Alkynes
In this study imidazolium salts conveniently functionalized with trialkoxysilyl groups either in the carbon backbone or in the nitrogen atom were complexed with Rh and incorporated into hybrid silica materials either by a sol-gel or a grafting process. Full characterization of the materials and the evaluation of their catalytic activities in the [2+2+2] cycloaddition of alkynes is reported.
O. El Bakouri, D. Cassú, M. Solà, T. Parella, A. Pla-Quintana and A. Roglans
Chem. Comm., 50, 8073 (2014). DOI
A new mild synthetic route to N-arylated pyridazinones from aryldiazonium salts
An efficient method for the synthesis of N-arylated pyridazinones from potassium 2-furantrifluoroborate and aryldiazonium salts is described. The reaction was run in water at 0–5 ºC in short reaction times and without any catalyst or additive. A mechanistic proposal is made based on the experimental data and DFT calculations.
E. Haraburda, O. Torres, T. Parella, M. Solà and A. Pla-Quintana
Chem. Eur. J., 20, 5034 (2014). DOI
Stereoselective Rhodium-Catalysed [2+2+2] Cycloaddition of Linear Allene–Ene/Yne–Allene Substrates: Reactivity and Theoretical Mechanistic Studies
The [2+2+2] cycloaddition reaction of Allene–ene–allene and allene–yne–allen substrates catalysed by the Wilkinson catalyst [RhCl(PPh3)3] was evaluated. Tricyclic structure which several contiguous stereogenic centres were formed in a diastereoselective manner and further Diels–Alder reaction yielded pentacyclic scaffolds.
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