5H-phenanthridin-6-one

The synthesis of selectively substituted benzoxepines from ortho-substituted aryl iodides and bromoenoates has been achieved by Lautens and coworkers by palladacycle alkylation followed by an intramolecular Heck reaction under the modified conditions reported in Eq. (8) for synthesis of l-(l-ethoxycarbonylmethy-lene)-9-methyl-4,5-dihydro-3-benzoxepine [8]. In the second example (Eq. 9) the palladium-bonded biphenylyl inserts diphenylacetylene to form 1,5-di-i-propyl-9,10-diphenylphenanthrene[9]. In the last case the synthesis of 4-methyl-5H-phenanthridin-6-one is achieved by palladium-catalyzed sequential C-C and C-N bond formation starting from o-iodotoluene and o-bromobenzamide [10]. 

In the presence of halides, yields of heterocyclisation products (carbazole (2) and 5H-phenanthridin-6-one (5)) were ca. 75-85 %, with a preference for 2 in the order Cl > Bf s F f, whereas the selectivity towards 5 was the reverse, F > Br = F > Cr. The yield of orf/to-aminobiphenyl (3), probably derived from the protonation of the intermediate nitrene complex, was strongly decreased. 

The first direct observation of atropisomers in this series was reported by NMR on 5-(2-methylphenyl)phenanthridin-6(5H)-one (446) in the presence of tris-[3-trifluoromethylhydroxymethylene-(+)-camphorato]euro-pium(III) (73JCS(CC)537). 

Banwell, M. G. Cowden, C. J. Mackay, M. F. 1994. Concise synthetic ronte to both enantiomeric forms of 2,3,4,4a-tetrahydro[l,3]dioxolo[4,5-j]phenanthridin-6(5H)-one. Tetracyclic skeleton associated with the narcissus alkaloids lycoricidine and narciclasine. J. Chem. Soc. Chem. Commun. 61-62. 

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