Metal-Catalyzed Oxidative Cyclizations of a,c-Biladiene Salts Bearing 1- and/or 19-Arylmethyl Substituents:  Macrocyclic Products and Their Chemistry

Abstract

Several 1-mono- and 1,19-bis(p-arylmethyl)-a,c-biladiene salts were prepared and subjected to either copper(II)- or chromium(III)-assisted oxidative cyclization to yield numerous products in which the 1- or 19- substituent is adapted, eliminated, or rearranged to other points on the tetrapyrrole. For example, cyclization using copper(II) acetate of 19-((ethoxycarbonyl)methyl)-2,3,7,8,12,13,17,18-octamethyl-19-(p-tolylmethyl)-a,c-biladiene dihydrobromide (25) yielded the copper(II) 20-((ethoxycarbonyl)methyl)-1-(p-tolylmethyl)-2,3,7,8,12,13,17,18-octamethyl-1,20-dihydroporphyrin (42), copper(II) 20-(ethoxycarbonyl)-3-methylidene-2,3,7,8,12,13,17,18-octamethyl-2-(p-tolylmethyl)chlorin (44), copper(II) 20-(ethoxycarbonyl)-2-methylidene-2,3,7,8,12,13,17,18-octamethyl-3-(p-tolylmethyl)chlorin (45), and three porphyrins: copper(II) 20-(ethoxycarbonyl)-2,3,7,8,12,13,17,18-octamethylporphyrin (3), copper(II) 2,3,7,8,12,13,17,18-octamethyl-20-p-tolylporphyrin (50), and copper(II) 20-(ethoxycarbonyl)-2,3,7,8,12,13,17,18-octamethyl-5-(p-tolylmethyl)porphyrin (47). Formation of porphyrin 47 and the intermediate chlorins 44 and 45 suggests the stepwise migration of the arylmethyl group from the 1-position in compound 42. The isolation of products from cyclization reactions of various 1,19-arylmethyl-substituted a,c-biladiene salts provides further insight into the mechanisms of metal-assisted oxidative cyclization of a,c-biladiene salts to give cyclic tetrapyrroles. Macrocyclizations of a,c-biladienes such as 25 using chromium(III) afford good yields of the metal-free 1-substituted compounds such as 43.

Syntheses and Functionalizations of Porphyrin Macrocycles

“…Fluorination reagents include N -fluoropyridinium triflates [69], cesium fluoroxysulfate [70], and fluorides of cobalt or silver [71]. N -Chlorosuccinimide (NCS) [72-77] or chlorine [64, 65] are normally used for chlorination, although HCl/H 2 O 2 [78] and PhSeCl 3 [79] have also been reported. Similarly, N -bromosuccinimide (NBS) [63, 64, 67, 80-84], bromine [64, 73, 85, 86], HBr/H 2 O 2 [66, 71], copper(II) bromide [85] and PhSeBr 3 [69] have been used for bromination of porphyrin macrocycles.…”

Biladienones from the Photooxidation of a meso-gem-Disubstituted Phlorin: Crystal and Molecular Structures of the 3N + O Coordinated Nickel(II) and Copper(II) Complexes

“…Phlorins are nonaromatic isomers of chlorins and are produced after reduction or addition of nucleophiles to the porphyrins macrocycle. − The stability of most phlorins is limited. Only in a few favorable cases, when stabilized by steric hindrance, ring deformation, or complexation by high valent metals, can these compounds be isolated in a pure state. − The general decomposition process is a simple oxidation to the parent porphyrin, but the irreversible meso addition of a carbon nucleophile, viz., an alkyl group, does not allow this reaction to proceed. We isolated such a phlorin ( 1 ) by addition of n -butyllithium to meso -tetraphenylporphyrin, and although highly unstable toward oxidation, it could be fully characterized.…”

Pyridyl-substituted porphyrins: I. Synthesis and basicity of monopyridylporphyrins

“…Methods based on transformations of key mono-or dipyrrole compounds into porphyrins ensure preparation of relatively simple symmetric tetrapyrrole macrorings. The optimal methods for the synthesis of more complex porphyrins with several different substituents in the macroring are those involving intermediate formation of open tetrapyrrole compounds.Depending on the oxidation state, linear tetrapyrrole compounds frequently used for the synthesis of porphyrins can be divided arbitrarily into three main groups: bilanes I, bilenes-b II, and biladienes-ac dihydrobromides III [1][2][3][4][5][6][7][8][9]. Increase of the number of meso-CH bridges in the system makes it more stable toward electrophiles.…”

“…Depending on the oxidation state, linear tetrapyrrole compounds frequently used for the synthesis of porphyrins can be divided arbitrarily into three main groups: bilanes I, bilenes-b II, and biladienes-ac dihydrobromides III [1][2][3][4][5][6][7][8][9]. Increase of the number of meso-CH bridges in the system makes it more stable toward electrophiles.…”

“…Lash and Roper [4] used biladienes-ac to obtain porphyrins containing two naphthyl groups in the macroring. Lin et al [5] synthesized porphyrin by cyclization of 1,19-arylmethylbiladieneac salts. A detailed review on the syntheses of porphyrins through biladienes was published in [10].…”