Ytterbium-Catalyzed Tandem Diels–Alder/Claisen Rearrangement/Decarboxylation of Hetero-Allenes for the Synthesis of Diarylmethanes

A tandem Diels–Alder reaction/Claisen rearrangement/decarboxylation strategy of N-allenamides (or aryloxyallenes) with 3-alkoxycarbonyl-2-pyrones has been developed for the efficient synthesis of diarylmethanes with moderate to good yields. The reaction exhibits good functional group tolerance and can be applied to late-stage modifications of known drug molecules. Mechanistic studies indicate that the ester group at the 3-position of 2-pyrones is essential, and the initial Diels–Alder reaction between the 2-pyrones and the proximal C=C bond of the N-allenamides (or aryloxyallenes) is crucial for the success of the reaction.