Phosphine-Catalyzed Addition/Cycloaddition Domino Reactions of β′-Acetoxy Allenoate: Highly Stereoselective Access to 2-Oxabicyclo[3.3.1]nonane and Cyclopenta[a]pyrrolizine

Two classes of phosphine-catalyzed addition/cycloaddition domino reactions of β'-acetoxy allenoate 1 have been developed. The reaction of 1 with 2-acyl-3-methyl-acrylonitrile 2 readily occurs to give 2-oxabicyclo[3.3.1]nonane 3, furnishing the β'-addition/[4 + 4] cycloaddition domino sequence. In this sequence, β'C of allenoate 1 is an electrophilic center, and its β'C and γC serve as a 1,4-dipole. When the other reaction partner is switched to 2-acyl-3-(2-pyrrole)-acrylonitrile 8, a γ-addition/[3 + 2] cycloaddition domino reaction is instead observed, in which allenoate 1 exhibits dual electrophilic reactivity of γC and 1,3-dipole chemical behavior of βC and β'C. Furthermore, both of these two asymmetric variants have also been achieved with up to 93% ee. The domino reactions presented in this report are valuable for highly stereoselective construction of complex structures under mild reaction conditions.