Porphyrins with exocyclic rings. Part 25: synthesis of porphyrins with a fused cyclic ether subunit from tetrahydro-4H-pyan-4-one
- Resource Type
- Article
- Authors
- Smith, Breland E.; Lash, Timothy D.
- Source
- Tetrahedron. Jun2010, Vol. 66 Issue 25, p4413-4422. 10p.
- Subject
- *PORPHYRINS
*ORGANIC synthesis
*CROWN ethers
*PYRAN
*KETONES
*OXIMES
*CONDENSATION
*CONFORMATIONAL analysis
- Language
- ISSN
- 0040-4020
Abstract: A novel porphyrin system with a fused dihydropyran ring has been synthesized from commercially available 4-oxotetrahydropyran. The cyclic ketone reacted with oximes derived from acetoacetate esters in the presence of zinc dust, sodium propionate, and propionic acid at 150–155°C to give good yields of 5-oxatetrahydroindoles. A low yield of a benzo-fused analog was also obtained using 4-oxochromanone as the starting reagent. Reaction of the b-annelated pyrroles with N-chlorosuccinimide gave the 7-chloro-derivatives and these underwent an acid catalyzed condensation with α-unsubstituted pyrroles to give dipyrrolic products linked by a dihydropyran moiety. Hydrogenolysis of a dipyrrole dibenzyl ester gave the corresponding dicarboxylic acid and this was converted into a dialdehyde by treatment with TFA–CH(OMe)3. MacDonald ‘2+2’ condensation with two different dipyrrylmethanes under optimized conditions afforded the porphyrin ethers in 30–36% yield. This approach provides a pilot study for the synthesis of porphyrin crown ether structures. In addition, insightful results on the conformations of dihydropyran-linked dipyrroles were obtained by careful examination of their proton NMR spectra in CDCl3 and DMSO-d 6. [Copyright &y& Elsevier]