Intramolecular Cycloaddition Reactions of ortho-Quinodimethanes in Organic Synthesis

This review delineates the scope and limitations of intramolecular cycloaddition reactions of ortho-quinodimethanes for the stereoselective synthesis of polycyclic ring systems containing at least one aromatic ring. A summary of the available routes (including in situ generation) to ortho-quinodimethanes is given first, followed by specific examples which illustrate the use of benzocyclobutenes, 3-isochromanones and ortho-tolyl-carbonyl compounds as ortho-quinodimethane precursors. Finally, several applications of intramolecular ortho-quinodimethane cycloadditions for the synthesis of natural products are described. 1. Introduction 2. Intramolecular Thermal Additions of Benzocyclobutenes 2.1. Olefinic and Acetylenic Systems as Dienophiles 2.2. Carbonyl, Imino, and Nitrile Systems as Dienophiles 2.3. Acetylene Cooligomerization 3. 3-Isochromanones as Masked ortho-Quinodimethanes 4. Photoenolization 5. Syntheses of Natural Products 5.1. Alkaloids 5.2. Steroids and Terpenoids 6. Conclusions