A [2 + 2] Cycloaddition Dimer and a Diels–Alder Adduct fromAlpinia katsumadai

An unusual katsumadain dimer via a [2 + 2] cycloaddition, katsumadain C (1), and a unique chalcone-diarylheptanoid adduct via a Diels–Alder reaction, calyxin Y (2) with novel carbon frameworks, were isolated from the seeds of Alpinia katsumadai. Their structures and relative configurations were determined by spectroscopic...