Rhodium mediated C-H bond functionalisation leading to carboxylate derivatives.

Carboxylic acids and their esters or lactones are among the most common functionalities, and a large number of fine chemicals are accessible from this functionality. Typical organic synthetic procedures towards carboxylic acids include oxidation of alcohols and aldehydes and hydrolysis of nitriles, while carboxylation of organic substrates containing C X bonds is perhaps the best established approach to carboxylic acids mediated by transition metal complexes. From an atom economy perspective, direct functionalization of C H bonds to C CO2R bonds is a highly desirable alternative, since it avoids classical functional group manipulations. Although scarce, such palladium catalysed reactions were recently reported. From a formal point of view, a COO moiety could be inserted into a C H bond by the combination of oxygenation and carbonylation involving simply O2 and CO as attractive and cheap substrates. In this line, 2-metallaoxetanes emerge as valuable candidates to test this possibility, since they could be obtained by oxygenation of olefins with dioxygen. Although the reactivity of 2-metallaoxetanes is currently in its infancy, two of them have been reported to be suitable for C X (X = N, O) bond formation, as shown for the reactions of 2-rhodaand 2-platina-oxetanes with acetonitrile and carbon monoxide, respectively. In this communication we describe new reactions leading to carboxylic acids and lactones, involving the stoichiometric functionalization of an allylic C H bond of cod with carbon monoxide and dioxygen which proceeds via a discrete 2-rhodaoxetane intermediate.