Useful Applications of Enantioselective (4 + 2)-Cycloaddition Reactions to the Synthesis of Chiral 1,2-Amino Alcohols, 1,2‑Diamines, and β‑Amino Acids

The scope of enantioselective (4 + 2)-cycloaddition reactions has been expanded to include reactive olefinic components that are equivalents of three inoperable and unstable ethylene derivatives: 1-hydroxy-2-aminoethylene, 1,2-diaminoethylene, and β-aminoacrylic acid. In this way, a variety of otherwise unavailable functionalized (4 + 2)-cycloadducts have been synthesized from 1,3-dienes with high enantioselectivity (92–98%) and in good yields. The research leading up to this synthetic advance has also produced some surprising insights on reactivity and positional selectivity in catalytic enantioselective (4 + 2)-cycloaddition.