Cleavage of nickel(II) octaethyl-2,3-dihydroxychlorin 3 with lead tetr
aacetate gives the novel octaethyl-2,3-secochlorin-2,3-dione system as
its nickel(II) complex 4, which on treatment with base cyclises to a
novel homoporphyrinone structure 5; electronic spectra are presented:
4 and 5 are seen as representing chromophores that may arise in chloro
phyll catabolism.