From Five to Seven: Ring Expansion of Monoazadiene Titanium Complexes by Insertion of Aldehydes, Ketones and Nitriles

The ring enlargement reactions at ambient temperatures of non C‐terminus substituted monoazabutadiene (η4−RN=CHCH=CH2) titanium complexes 2 are investigated. The insertion of aldehydes/ketones (five examples) and nitriles (four examples) into the Ti−C bonds result in expansion of the five‐membered rings to uncommon seven‐membered titanacycles 3 and 4 in good yields. These new compounds are fully characterized by NMR spectroscopy and single‐crystal X‐ray diffraction. In subsequent reactions, the seven‐membered ring systems are protolyzed and the released organic fragments are isolated. Whereas the aldehyde/ketone insertion products 3 form substituted δ‐amino alcohols 5 after reduction with NaBH3CN, the nitrile insertion products 4 form substituted pyrroles 6 via cyclization. Two more, please! Insertion of carbonyl compounds and nitriles into the Ti−C bond of non C‐terminus substituted monoazabutadiene titanium complexes result in expansion of the five‐membered rings to uncommon seven‐membered titanacycles. In subsequent reactions, the seven‐membered ring systems are protolyzed and amino alcohols and pyrroles are isolated.