Dibenzofurans ring-cleavage

Gesell M, E Hammer, A Mikolasch (2004) Oxidation and ring cleavage of dibenzofuran by the filamentous fungus Paecilomyces lilacinus. Arch Microbiol 182 51-59. 

Strubel V, K-H Engesser, P Fischer, H-J Knackmuss (1991) 3-(2-hydroxyphenyl)catechol as substrate for proximal meta ring cleavage in dibenzofuran degradation by Brevibacterium sp. strain DPO 1361. J Bacterial 173 1932-1937. 

Fortnagel, P., Harms, H., Wittich, R.-M., Francke, W., Krohn, S. and Meyer, H. (1989). Cleavage of dibenzofuran and dibenzo-p-dioxin ring systems by a Pseudomonas bacterium, Naturwissenschaften, 76, 222-223. 

Cleavage of the hetero ring of dibenzofuran by Li followed by the addition of ketones offers a useful route to 6,6-disubstituted dibenzo[/>,<7]pyrans 13 <06JOC8291> and a photochemical rearrangement of naphtho[2,3-b]benzofuranones was used to prepare intensely fluorescent indeno[ 1,2-/>]benzo[4,5-e]pyranones 14 <060BC3406>. 

In addition, the downfield shifts of the signals due to C(19 ), C(15 ), and C(20 ), in comparison with those of the corresponding carbons of peceylanine (388), are suggestive of formation of a lactone ring. These results are accommodated by formation of a bond between N(l ) and C(16 ), following cleavage of the C(7 )-C(16 ) bond of peceylanine, followed by intramolecular lactone formation from attack of the carboxy-late function on the epoxide moiety. Ceylanicine (391) was shown by the spectral data to bear a close similarity to pelankine (389), with the monomeric units linked to incorporate a similar central dibenzofuran unit. The main departures concern the cleavage of the C(3 )-N(4 ) bond, and the formation of a lactone from reaction of the C(16 )-carboxylate function with the 19, 20 -epoxide moiety. The third bisindole 392 was readily shown to be the -demethyl derivative of peceyline from the spectral data. 

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