Studies in chlorin chemistry. II. A versatile synthesis of dihydrodipyrrins.
[reaction: see text] Dihydrodipyrrins are key building blocks for the synthesis of hydroporphyrins, many of which have important biological activity. The title compounds were prepared in stereo- and regioselective fashion by a three-step sequence consisting of (1) Pd(0)-catalyzed coupling-cyclization of 2-iodopyrroles with gamma-alkynoic acids to afford enelactones of the desired substitution pattern, (2) methylenation at the lactone carbonyl group employing the Petasis reagent, and (3) in situ enol-ether hydrolysis and amination of the resultant 1,4-diketone to close the pyrroline ring (nine examples). Yields for each step were generally high, although in substrates not blocked by geminal substitution aromatization to a dipyrromethane is a competing side reaction.
O'Neal
William G
WG
Burke Chemical Laboratory, Dartmouth College, Hanover, New Hampshire 03755, USA.
Roberts
William P
WP
Ghosh
Indranath
I
Jacobi
Peter A
PA
D008968:Molecular Conformation; D011166:Porphyrins / Q000138:chemical synthesis*
D011166:Porphyrins