An Unequivocal Synthesis of the Ring-A,B Dihydropyrromethenone of Phytochrome.

Abstract Dihydropyrromethenone 1b (R = p -methoxybenzyl), a potential precursor for the synthesis of phytochrome ( 3 ), has been prepared in enantiomerically pure form beginning with the homochiral acetylenic lactone 18 .