ISOPHLORINS - MOLECULES AT THE CROSSROADS OF PORPHYRIN AND ANNULENE CHEMISTRY

The isophlorins already discussed by Woodward in connection with chlorophyll synthesis are Janus-faced-on one hand porphyrins (N,N'-dihydroporphyrins) and on the other true annulenes ([20]annulenes not conforming to the Huckel rule)-and as such are structurally particularly interesting. Whereas isophlorins not substituted at NH have evaded discovery and synthesis, the N,N',N'',N'''-tetramethyloctaethylisophlorin (1, R = CH3) has been prepared by two-electron reduction of the known N,N',N'',N'''-tetramethyloctaethylporphyrin dication.