Rhodium‐Catalyzed [2+2+2] Cycloaddition Reactions of Linear Allene–Ene–Ynes to afford Fused Tricyclic Scaffolds: Insights into the Mechanism

• Published in: Chemistry : a European journal 2017-10, Vol.23 (59), p.14889-14899
• Main Authors: Cassú, Daniel, Parella, Teodor, Solà, Miquel, Pla‐Quintana, Anna, Roglans, Anna
• Format: Article
• Language: English
• Subjects: Addition reactions; Alkenes; Alkynes; Allene; allenes; Catalysis; Chemical reactions; Chemistry; Cycloaddition; density functional calculations; Density functionals; Funcional de densitat, Teoria del; Mecanismes de reacció (Química); Reaccions d'addició; reaction mechanisms; Reaction mechanisms (Chemistry); Rhodium; Rodi; Scaffolds; Stereoselectivity; Substrates; YneS protein
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201703194

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. Translation S′ha preparat satisfactòriament una sèrie de substrats 3 a–3 h de cadena oberta contenint un al⋅lè, un doble enllaç i un alquí i s'ha avaluat la seva reacció de cicloaddició [2+2+2] catalitzada per rodi. La cicloaddició és quimioselectiva degut a què només el doble enllaç intern de l′al⋅lè reacciona per donar un sistema tricíclic fusionat amb un doble enllaç exocíclic. L′estereoselectivitat del procés depèn del sistema catalític emprat. La diferent reactivitat entre l′al⋅lè, l′alquè i l′alquí s'ha estudiat per primer cop mitjançant càlculs teòrics basats en la teoria del funcional de la densitat. Aquest estudi mecanístic permet determinar l′ordre en què les insaturacions participen en el cicle catalític. Fused tricyclic scaffolds: Three carbon‐based unsaturated moieties (allene–alkyne–alkene) have been jointly involved in [2+2+2] cycloaddition reactions under rhodium catalysis. The ligands on the catalyst affect the diastereoselectivity of the process. DFT calculations rationalize these selectivity issues and the order in which the different unsaturated groups take part in the catalytic cycle.