Pd(0)-Catalyzed Cycloaddition of Alkylidene Cyclopropanes to Allenes

Significance

In the presence of a Pd(0)-phosphite ligand catalyst system, tethered allenyl alkyli­dene cyclopropanes undergo an intramolecular [3+2] cycloaddition to generate bicyclic [3.3.0] ring systems in good to excellent yield and with fair to excellent diastereoselectivity. Heteroatom-tethered systems (N, O) afforded the products with the highest levels of diastereoselectivity. It was found that rigorous deoxygenation of the reaction was necessary to prevent ligand oxidation and promote catalyst turnover. The substitutents on the allene were found to greatly influence the product diastereoselectivity, as the introduction of terminal methyl groups enhanced the selectivity in the malonate-tethered cases [X = C(CO₂Et)₂].