Intermolecular Aminocarbonylation of Alkenes using Concerted Cycloadditions of Iminoisocyanates

Abstract

The aminocarbonylation of alkenes is a powerful method for accessing the β-amino carbonyl motif that remains underdeveloped. Herein, the development of intermolecular aminocarbonylation reactivity of iminoisocyanates with alkenes is presented. This includes the discovery of a fluorenone-derived reagent, which was effective for many alkene classes and facilitated derivatization. Electron-rich substrates were most reactive, and this indicated that the LUMO of the iminoisocyanate is reacting with the HOMO of the alkene. Computational and experimental results support a concerted asynchronous [3 + 2] cycloaddition involving an iminoisocyanate, which was observed for the first time by FTIR under the reaction conditions. The products of this reaction are complex azomethine imines, which are precursors to valuable β-amino carbonyl compounds such as β-amino amides and esters, pyrazolones, and bicyclic pyrazolidinones. A kinetic resolution of the azomethine imines by enantioselective reduction (s = 13-43) allows access to enantioenriched products. Overall, this work provides a new tool to convert alkenes into β-amino carbonyl compounds.