Synthesis of C4C5 Cycloalkyl‐Fused and C6‐Modified Chromans via ortho ‐Quinone Methides

Starting from 3,5‐dimethoxybenzaldehyde, some functionalized 2,3,4‐trisubstituted tricyclic 4,5‐cycloalkyl‐fused and 6‐modified chromans could be prepared via ortho ‐quinone methides ( o ‐QMs)/hetero‐Diels–Alder (HDA) reactions of the appropriate precursors. The bromide at C6 served as a handle for introducing other substituents through palladium‐catalyzed cross‐coupling reactions and other functional‐group transformations. Moderate to high yields (up to 80 %) and diastereoselectivities (up to >99:1) could be obtained under [PtCl 4 ] catalysis. The preferred endo transition state during the cycloaddition reaction played an important role in governing the stereochemical outcomes at C2C3C4. The configurationally fixed E geometry of the bicyclic o ‐QMs influenced the cycloaddition reactions to favor the C2C4 cis relationship.