Tetrahydrofluorenyl Rhodium Complexes: Positive Impact of P-Methoxybenzyl Substituent on Catalytic Annulation Reactions

Rhodium complex based on 9-(p-methoxybenzyl)-1,2,3,4- tetrahydrofluorenyl ligand was found to be an efficient catalyst for various C–H annulation reactions such as couplings of benzoic acids with alkynes, pivaloyl hydroxamate with alkenes, or the tandem reaction of p-anisaldehyde and p-toluidine with tolane. The catalyst demonstrated higher catalytic performance than the unsubstituted analog due to the stabilization of the rhodium–tetrahydrofluorenyl bond. Tetrahydrofluorenyl rhodium complexes also effectively catalyzed the synthesis of tetramethyl thiophene-2,3,4,5- tetracarboxylate from elemental sulfur and dimethyl acetylenedicarboxylate.