Synthesis of chroman derivatives by the ring expansion reaction of spirodienones, and an assessment of their plant growth inhibition

Lewis acid-promoted 1,2-shift rearrangement reactions of the spirodienones, generated by the anodic oxidation of phenol derivatives, provided corresponding chromans. In addition to steric repulsion, electron-donating or withdrawing characteristics of the arylic substituents controlled the direction of the rearrangements. The plant growth inhibitory activity of several chroman derivatives was evaluated. In contrast to apparent inhibitions of 21c and 22c against both cress and oat. the selective activity against coleoptile and root of oat was observed in 21a, 21b, and 22d. Interestingly, the regioisomer 22b of 21b showed no activity.