21-Carba-23-oxaporphyrinoids and 21-oxo-21-carba-23-oxaporphyrinoids: macrocyclic π-conjugation involving the carbonyl moiety

Abstract

A rational synthesis using carba analogues of tripyrrane and 1,3-bis(arylhydroxymethyl)furan as synthons resulted in the formation of 21-carba-23-oxaporphyrin and 21-carba-23-oxachlorin.The molecular design preserves all essential virtues of 21-oxaporphyrin architecture allowing...

Organometallic Chemistry within the Structured Environment Provided by the Macrocyclic Cores of Carbaporphyrins and Related Systems

“…Oxidation with DDQ afforded the related thiacarbaporphyrin 46a in 25% yield together with the quinone addition product 47 . Very recently, related oxacarbachlorins 45b and oxacarbaporphyrins 46b were prepared in a similar fashion [ 109 ].…”

“…The system has 20 and 24 π-electron pathways, structures 178 a and 178 b that could result in antiaromatic character, but dipolar contributors such as 178′ provide 18π electron circuits that promote a degree of aromatic character [ 161 ]. Recently, oxacarbaporphyrin 180 was reported to undergo air oxidation to form a similar nonaromatic keto-structure 181 [ 109 ]. In addition, oxacarbachlorin 182 was oxidized with silver(I) acetate to give a structurally related aromatic derivative 183 ; in this case, the competing antiaromatic pathways are no longer present [ 109 ].…”

“…Recently, oxacarbaporphyrin 180 was reported to undergo air oxidation to form a similar nonaromatic keto-structure 181 [ 109 ]. In addition, oxacarbachlorin 182 was oxidized with silver(I) acetate to give a structurally related aromatic derivative 183 ; in this case, the competing antiaromatic pathways are no longer present [ 109 ].…”

21‐Carba‐23‐selenaporphyrinoid Dyads—An Azepine Unit as a Merging Motif

“…In contrast, 10,15-ditolyl-21-carba-23-oxaporphyrin exists exclusively as tautomer II in solution (ΔE = 6.8 kcal/mol). [16] The oxidation of 21-carba-23-selenaporphyrinoids 13 or 14 resulted in chemistry unprecedented for carbaporphyrinoids. Thus, the reaction of 21-carba-23-selenaporphyrin 13 ') carbon atoms with a parallel-displaced geometry, is similar to previously reported bis(21-carba-23-thiaporphyrin).…”

“…The 13 C chemical shift for C( 21) of 18 at 187.5 ppm unambiguously indicates the presence of the carbonyl group in the dyad. [16] DFT calculations were carried out for the hydroxy and keto tautomers of compound 18. The significant energy difference between tautomers 18 and 18-OH (Scheme S9), which is 29.2 kcal/mol, is consistent with the preferential formation of 18 in solution.…”