Cp2Ti(II) Mediated Rearrangement of Cyclopropyl Imines

Ti-catalyzed oxidative alkyne carboamination with alkenes and azo compounds can yield either alpha,beta-unsaturated imines or cyclopropyl imines through a common azatitanacyclo-hexene intermediate. Herein, we report the synthesis of a model azatitanacyclohexene complex (3) through the ring-opening of a cyclopropyl imine with Cp2Ti(BTMSA) (BTMSA = bis-(trimethylsilyl)acetylene). 3 readily undergoes thermal or reduc-tant-catalyzed ring contraction to an azatitanacyclopentene (4), analogous to the proposed mechanism for forming alpha,beta-unsaturated imines in the catalytic reaction. A cyclopropyl imine or an alpha,beta-unsaturated imine could be liberated via the oxidation of 3 or 4 with azobenzene, respectively, further implicating the role of these metallacycles in the Ti-catalyzed carboamination reaction.

Automated summary

This article reports the Ti-catalyzed oxidative alkyne carboamination reaction between alkenes and azo compounds, which can yield either alpha,beta-unsaturated imines or cyclopropyl imines through a common azatitanacyclo-hexene intermediate. A model azatitanacyclohexene complex (3) was synthesized through the ring-opening of a cyclopropyl imine with Cp2Ti(BTMSA) (BTMSA = bis-(trimethylsilyl)acetylene). Complex 3 readily undergoes ring contraction to an azatitanacyclopentene (4), analogous to the proposed mechanism for forming alpha,beta-unsaturated imines in the catalytic reaction. The liberation of cyclopropyl imine or alpha,beta-unsaturated imine through the oxidation of 3 or 4 with azobenzene further confirms the role of these metallacycles in the Ti-catalyzed carboamination reaction.