The impact of oxygen on the reaction was investigated, leading to the observation that full conversion was observed for the model reaction within 15 min in pure O2 atmosphere, whereas the conversion under air was solely 24%. Next, deuterated benzyl alcohol-α,α-D2 was used as substrate. No drop of deuterium content was detected in the product. Surprisingly, if 18 O-enriched benzyl alcohol was employed as starting material, a massive drop in 18 O-content was observed in the in situ generated benzaldehyde (Scheme 2). This is attributed to an exchange with oxygen from air, underlining the crucial role of O2 in this transformation.