Dibenzo pyranones

The palladium catalyzed benzannulation reaction, described by Yamamoto, was successfully extended to the synthesis of condensed pyranone derivatives. The precursor to the cyclization underwent the benzannulation spontaneously under the applied Sonogashira coupling conditions (8.40.) on formation, to give the desired dibenzo />,ri pyranone. The functionalities tolerated in the process include unsaturated bonds and polar functional groups, such as hydroxyl.52... 

S,.S)-Bissetone (28), when traced back to building block 27, only lacks the 3-carbon branch, i. e. acetone. Indeed, the lithium enolate of acetone proved to be a suitable three-carbon synthon attacking the carbonyl function with a 4 1 preference from the proaxial side (27 -> 30). The benzoyl group shift directly following the attack elaborates the desired 2-oxopropyl-branehed tetrahydro-pyranone 31, the dibenzoate of bissetone in fact, from which the parent compound is generated simply by de-O-benzoylation (48) ... 

A one-pot synthesis of dibenzo[f>,d]pyranones from the aryl propenoate 17 proceeds via sequential Sonogashira coupling and an intramolecular benzannulation. <02JOC5138>. 

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>. 

Several approaches to dibenzo[b,c/]pyranones have been reported. The simplest, with a 45% yield, is the TiCVphotocatalysed oxidation of phenanthrene <06CC2804>. 

Remote metalation of biaryls and m-teraryls provides a general synthesis of substituted and condensed fluorenones (eq47). Similarly, biaryl 0-carbamates undergo remote metalation and anionic Fries rearrangement to 2-hydroxy-2 -carboxamidobiaryls, which are efficiently transformed into dibenzo[fc,i/]pyranones. ... 

Wang, W. (1991) Directed ortho and remote aromatic metalation synthesis of highly substituted biaryls, dibenzo(b,d)pyranones and 3,3 -substituted-l,l -bi-2-naphthols. M.Sc. Thesis. University of Waterloo, Canada. 

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