Imine allylation from the amine oxidation level via transfer hydrogenative coupling of allyl acetate
Final Report Abstract
The proposed imine allylation from the amine oxidation level under hydrogen autotransfer conditions with allyl acetate, which was focus of the research proposal, which would have given access to chiral amines, could surprisingly not be realized. Although a number of catalytic systems, reaction conditions, substrates, and additives were probed, desired product was never observed. Instead two other projects were realized. In the asymmetric direct prenylation of N-acyl pyrrolidines via iridium-catalyzed sp3 C H activation allene insertion, yields of up to 64% were reached using N-1- adamantanecarbonylpyrrolidine and 1,1-dimethylallene. Here, a catalyst assembled from [Ir(cod)2]BArF and diphenylphosphinoferrocene (dppf) in cyclohexane enabled the reaction. In addition, an enantioselective version of this reaction allowed for the formation of the respective product in 94 % ee, giving rise to a precursor to L-proline. Hence, this reaction represents a ‘detour’ to chiral amines as the aspired imine allylation could not be accomplished. The second project represents a rare example of the use of methanol as a C1-feedstock in catalytic C-C bond formation beyond hydroformylation. This iridium-catalyzed hydrohydroxymethylation is catalyzed by a preformed cyclometallated π-allyl iridium C,O-benzoate complex derived from [Ir(cod)Cl]2, allyl acetate, 3-nitrobenzoic acid and dppf of which single crystals could be gained and the X-ray structure could be determined. The iridium-catalyzed coupling of 1,1-disubstituted allenes with methanol yields homoallylic neopentyl alcohols and proceeds via a kinetically significant C-H cleavage event. To further increase the relevance of this reaction, future studies might focus on related enantio- and diastereoselective alcohol-unsaturate C-C coupling and on an extension to other allyl precursors such as alkynes, dienes, or allyl acetate.
