Progress on the Synthesis of Extended PI System Metallotetrabenzporphyrins.

摘要

In an ongoing effort to examine the spectral and electrochemical properties and potential catalytic activity of porphyrins with extended Pi-systems, a synthetic route to the fluorinated 1,2-naphthoporphyrin 4b was investigated. The synthesis involved Diels-Alder addition of hexafluoro-1,2-naphthyne to N-trimethylsilylpyrrole followed by hydrogenation of the olefinic double bond and removal of the trimethysilyl protecting group to generate the phenanthrene-1,4-imine 14. Retro Diels-Alder reaction of 14 would produce hexafluorobenz (e) isoindole 15, which should form the porphyrin 4b on heating with zinc acetate and paraformaldehyde. The Diels-Alder-hydrogenation-deprotection sequence worked in the case of the benzo series and 20 was obtained in reasonable yield. However, in the 1,2-naphtho series, the same reaction sequence gave 14 in very low yield. p-Methoxybenzylpyrrole has been synthesized and characterized. The p-methoxybenzl group may be a superior blocking group for the pyrrole nitrogen atom in that its removal should be effected under milder conditions than the trimethylsily or benzyl group. It is, therefore, recommended that synthetic efforts on this project be focused on the p-methoxybenzyl series of compounds which should lead to more facile synthesis of the phenanthrene-1,4-imine 14.