Dedicated to Prof. Dr. Lutz F. Tietze with deep respect and admiration on the occasion of his 80th birthday
Abstract
This review summarizes recent developments in the area of Brønsted acid catalyzed, enantioselective cycloadditions of ortho-quinone methides, ortho-quinone methide imines as well as heterocyclic indole- and pyrrole-based methides. In a straightforward and single-step transformation complex polycyclic N- and O-heterocyclic scaffolds are accessible, with typically good yields and excellent stereocontrol, from simple benzyl and heterobenzyl alcohols upon acid-catalyzed dehydration. The transient precursors are hydrogen-bonded to a chiral Brønsted acid which controls the enantioselectivity of the process.
1 Introduction
2 Cycloadditions of ortho-Quinone Methides
2.1 Brønsted Acid Catalyzed Processes
2.2 Cooperative Brønsted Acid/Transition-Metal-Catalyzed Processes
3 Cycloadditions of ortho-Quinone Methide Imines
4 Cycloadditions of Indolyl-3-methides
5 Cycloadditions of Indolyl-2-methides
5.1 Brønsted Acid Catalyzed Processes
5.2 Cooperative Brønsted Acid/Transition-Metal-Catalyzed Processes
6 Cycloadditions of Pyrrolyl-2-methides
7 Cycloadditions of Pyrrolyl-3-methides
8 Conclusions
Key words
cycloaddition - heterocycles - indoles - pyrroles - chromans - enantioselectivity - Brønsted acid catalysis