Imines 4 cyclize stereoselectively to dihydroindoles 2 upon use of a Li or Na alkoxide- alcohol combination. Depending on the type of alcohol applied either cis (2C) or trans (2 T) spiroindolines 2 are formed. In case of imines 4 derived from electron-rich aromatic aldehydes the formation of 2 occurs also thermally. With Lewis acid/catalysis cyclization 4→ 2 proceeds in a less stereoselective manner. The stereochemistry of 2 follows from ...
