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 Hückel 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 , RCH 3 ) has been prepared by two‐electron reduction of the known N , N ′, N ″, N ″′‐tetramethyloctaethylporphyrin dication.