Copper‐Catalyzed α,β‐Regioselective (2+4) Cycloaddition of Propargylic Esters

Abstract A copper‐catalyzed α,β‐regioselective (2+4) cycloaddition of propargylic esters with o ‐hydroxyphenyl substituted secondary phosphine oxides (SPOs) was established, which afforded a series of phosphorus‐containing six‐membered heterocycles in high yields. This reaction represents the first α,β‐regioselective (2+n) cycloaddition of propargylic esters via the intermediates of copper‐allenylidenes, which will enrich the chemistry of propargylic esters and copper‐allenylidenes. Moreover, this work also represents the first application of o ‐hydroxyphenyl substituted SPOs as 1,4‐dinucleophiles in (2+4) cycloadditions, which provides a useful protocol for the synthesis of phosphorus‐containing six‐membered heterocycles with potential bioactivity.