Ylide is the key: The phosphane‐catalyzed [3+2] annulation of 2 a with aromatic aldehydes 1 to form tetrahydrofurans 3 in moderate to excellent yields is described (see scheme). This reaction represents an efficient and convergent one‐step route toward the construction of tetrahydrofurans and demonstrates a distinctive reactivity pattern of γ‐substituted allenoates with aldehydes.

No abstract

No abstract

A novel phosphine-mediated reductive cyclopropanation between alpha-substituted allenoates 2 and aldehydes 1 is described. It represents a new member of the allene-based annulations, which provides facile and efficient access to highly functionalized cyclopropanes 3 from simple and readily available starting materials. It also unveils an unprecedented reactivity pattern of allenoates with aldehydes.

The phosphine-mediated olefination of aldehydes with electron-deficient allenes to afford trisubstituted conjugated dienes in fair to excellent yields with high E-selectivity is described. The reaction represents a new reactivity pattern of allenes with aldehydes and also provides a highly stereoselective synthetic method for preparing conjugated dienes. In the reaction, the phosphine acts as a nucleophilic promoter to generate in situ an active phosphorus ylide which mediates the intermolecular olefination.