Nucleophilic Addition of Grignard Reagents to 3-Acylindoles: Stereoselective Synthesis of Highly Substituted Indoline Scaffolds

3-Acylindoles undergo nucleophilic-type reactions with Grignard reagents to efficiently afford either cis- or trans-substituted indolines, depending on the different quenching procedures. The enolate intermediate could be trapped by aryl acyl chlorides to provide indolines bearing a quaternary carbon center with high stereoselectivity. In contrast, the use of benzyl bromide as an electrophile results in the fragmentation of the indole ring. The indoline products could be easily transformed Into indoles through oxidation with DDQ in a one-pot manner.