Iron Porphyrin-Catalyzed Olefination of Ketenes with Diazoacetate for the Enantioselective Synthesis of Allenes

摘要

We have developed an efficient method for the synthesis of allenes under neutral conditions by olefination of ketenes with EDA in the presence of Ph_3P and catalytic Fe(TCP)-Cl for the first time. We have also realized its asymmetric version and found that, by employing chiral phosphine instead of PPh_3, chiral allenes could be synthesized with high enantioselectivities (93-98% ee) in good yields, providing an easy access to optically active allenic esters. In addition, the results described here confirmed that the mechanism involves ylide olefination. The high enantio-selectivity, the neutral condition, and the fact that the phosphine could be recovered and reused make the current method potentially useful in organic synthesis.