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Access to Substituted Indenol Ethers via a Regioselective Intermolecular Carbopalladation Cascade
preprintsubmitted on 18.12.2019, 19:43 and posted on 23.12.2019, 20:16 by Brandon L. Coles-Taylor, Maximilian S. McCallum, Andrés G. Muñoz, Brian Michel
Alkyne carbopalladation reactions represent a powerful approach to generating multiple new C–C bonds and substituted alkenes, however regioselectivity is often challenging for intermolecular variants. By utilizing ynol ethers as polarized alkynes we observe complete regiocontrol of migratory insertion with Pd–Ar species. A Heck reaction was used to turn-over the catalytic cycle by intercepting the vinyl-Pd adduct of carbopalladation with a pendant alkene. When using o-iodo styrenes substrates the resulting products are oligosubstituted 1-indenol ethers with defined stereochemistry based on the initial alkene geometry. By blocking β-hydride elimination we demonstrated C–H and C–C reductive elimination steps for catalyst turnover. Herein we report the optimization of reaction conditions, scope, and alternative termination steps.