Palladaelectro-catalyzed olefination reaction: distal and asymmetric approach

Abstract

One of the most traditional C-H activation reaction, Fujiwara-Moritani reaction requires stoichiometric metal oxidant. Electro-organic chemistry provides a greener alternative, where electron is used as the redox equivalent. Site specific C-H activation coud be achieved through the usage of directing groups (DGs). However, in thermal condition, site specificity could be severely hampered due to molecular bending/rotating motion of DGs and cleavage of DGs through trans esterification with the solvent molecules. Electro-organic reaction proceeds through benign reaction conditions so C-H activation can even occur in room temperature avoiding thus circumventing all issues related to thermal C-H activation. We envisioned that we might obtain superior site selectivity in meta-para sp2-H activation. Similarly improved enantioselectivity could be observed in case of biryl oxime which is designed to have internal DG. Using phenylacetic acid scaffold as model substrate, m-exclusive (meta: others > 20:1) and para-exclusive (para: others> 20:1) olefinated product was obtained at respective current conditions. Superior enantioselectivity of e.r. 99:1 was obtained for atroposelective olefination for biaryl-oxime (5-dimethoxy-2-(naphthalen-1-yl)benzaldehyde O-methyl oxime) at 0.4 mA using C as anode and Ni as cathode. Few substrate scopes were explored based on the current optimized electrochemical condition.