Metal-catalyzed oxidative cyclizations of a,c-biladiene salts bearing 1- and/or 19-arylmethyl substituents: Macrocyclic products and their chemistry
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.
Publication Source (Journal or Book title)
Journal of Organic Chemistry
Lin, J., Gerzevske, K., Liddell, P., Senge, M., Olmstead, M., Khoury, R., Weeth, B., Tsao, S., & Smith, K. (1997). Metal-catalyzed oxidative cyclizations of a,c-biladiene salts bearing 1- and/or 19-arylmethyl substituents: Macrocyclic products and their chemistry. Journal of Organic Chemistry, 62 (13), 4266-4276. https://doi.org/10.1021/jo9619138