Catalytic Phosphine-Enabled Direct δ-Addition of Substituted Allenoates to Nitroalkenes: A Route to 1,3-Dienes and 1,3,5-Trienes

Conjugated polyene represents a ubiquitous structural motif found in natural products and pharmaceutical agents. In this study, we demonstrate that γ-substituted allenoates can act as nucleophilic C4 synthon equivalents of dienes under phosphine catalysis, enabling their efficient addition with nitroalkenes to afford β-nitro 1,3-diene derivatives in moderate to good yields. This transformation features a remarkably broad substrate scope and good functional group compatibility, and it can be applied to the late-stage functionalization of complex natural product derivatives. The utility of the resulting β-nitro conjugated dienes is further demonstrated through subsequent transformations, affording a diverse library of conjugated triene compounds. A plausible reaction mechanism along with representative applications are also discussed.