The influence of a m- or p-polar substituent in 1-aryl 2-phenyl propanones, on addition reactions with CH3MgBr in ether at 30° has been investigated. The invariability of asymmetric induction as a function of substituent, and the correlation of rate constant ratios with Hammett σ constants (π = 0,24, r = 0,97), are consistent with a four-centre pericyclic concerted mechanism with concomitant departure
photocatalytic metal-free cross-coupling of benzylic and aldehydic C–H bonds by synergistic catalysis of organophotocatalyst 4CzIPN and a thiol, which affords the corresponding α-aryl ketones in acceptable yields along with hydrogen evolution. The mechanistic investigation indicates a radical–radical coupling to give an intermediary alcohol, followed by an acceptorless alcohol dehydrogenation.