Generation and cycloadditions of tetrahydrofuryl, pyranyl, and oxepanyl-2-imminium methylides

Cycloaddition of Heteroatom-Substituted 2-Azaallyl Anions with Alkenes. Synthesis of 1-Pyrrolines and Bridged Azabicyclic Compounds

“…The cycloadditions of aryl-substituted nitrile ylides ArC⋮N(+)C(−)HR with electron-poor dipolarophiles have been widely studied. Nitrile ylides without aromatic substitution are rare. , Pathway b shows the use of heteroatom-substituted azomethine ylides 3 as synthetic equivalents of nitrile ylides in cycloadditions with electron-poor dipolarophiles, requiring loss of the heteroatom after cycloaddition to install the imine functionality, i.e., 4 → 2 . − Pathway c shows the proposed use of heteroatom-substituted 2-azaallyl anions 5 to synthesize 1-pyrrolines. The cycloaddition of 5 with an alkene would produce the 1-lithiopyrrolidine 6 , which should readily β-eliminate to produce the desired 1-pyrroline 2 .…”

Synthesis of Spirocyclic Ethers

“…The lithium salt of lactone 272 was then further treated with dimethyl acetylenedicarboxylate (DMAD, 273) to provide the spiro ether 274 in 20% yield. Since then, other 1,3-cycloadditions yielding spiro heterocycles have been reported by Fishwick, 102 Howe, 103 and others. 104…”

Ruthenium-Catalyzed Intramolecular Double Hydrofunctionalization of Alkynes. Synthesis of Spirocyclic Hemiaminal Ethers and Their Lewis Acid-Mediated Cleavage/Nucleophilic Addition

“…Unfortunately, these classical approaches typically involve multistep preparation of cyclization precursors. Several groups have described the synthesis of spiroaminals through cycloaddition reactions of exocyclic imines and their equivalents . Suárez et al.…”