Rotational isomerization of 3-substituents in synthetic chlorophyll derivatives. Issue 42 (20th October 2016)

• Record Type: Journal Article
• Authors: Tamiaki, Hitoshi; Mizutani, Keisuke; Sasaki, Shin-ichi; Tatebe, Tomohiro
• Is Part Of: Tetrahedron. Volume 72:Issue 42(2016)
• Page Start: 6626
• Page End: 6633
• Publication Date: 2016-10-20
• Subjects: Atropisomer -- Conformational restriction -- NMR spectroscopy -- Pyropheophorbide -- Rotamer -- Steric repulsion; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tet.2016.08.079
• Languages: English
• ISSNs: 0040-4020

Abstract

Abstract: Methyl pyropheophorbides- a possessing a (pseudo)planar substituent at the 3-position were prepared from naturally occurring chlorophyll- a . Some of the semisynthetic π-conjugates with the chlorin skeleton took two atropisomeric conformations for the sterically demanding 3-substituents, CONMe2, NHCOMe, C[CHC(CN)2 ]C(CN)2, and Ph(2, 3, 4, 5-Ph4 ). Their rotational isomerization in a solution was analyzed by 1 H NMR and HPLC. Zinc complex of the 3-aryl-chlorin gave a large energy barrier for the rotation of the C3C3 1 single bond (estimated Δ G ‡ =108 kJ mol −1 at 20 °C) and the atropisomerically pure conformers were separated at room temperature. Graphical abstract: