Cascade dearomative [4+2] cycloaddition of indoles with in situ generated ortho-quinone methides: practical access to divergent indoline-fused polycycles

A rationally designed cascade dearomative [4 + 2] cycloaddition of indoles with in situ generated ortho-quinone methide (o-QM) provides a practical, atom and step economical access to diverse indoline-fused polycycles with high yields and excellent diastereoselectivity in one step. These polycyclic indolines feature divergent [6-6-5] and [6-5-5] tricyclic core skeletons bearing three contiguous stereogenic centers. Appealingly, most of the products precipitating in ethanol solution, the use of room temperature, easy handling, broad substrate scope and gram-scale synthesis make this transformation an environmentally benign, effective and attractive method for the synthesis of polycyclic indolines.

Automated summary

A cascade dearomative [4 + 2] cycloaddition reaction has been developed for the synthesis of diverse indoline-fused polycycles with high yields and excellent diastereoselectivity. The method is easy to handle, has a broad substrate scope, and can be conducted under environmentally benign conditions.