Facile Redox Interconversion of 6, 11‐Diphenyldibenzo[b, f][1, 4]diazocine and 2‐(2‐Aminophenyl)‐1, 3‐diphenylisoindole: Reversible SET Ring Contraction and Expansion Processes1. Issue 33 (14th October 2014)

• Record Type: Journal Article
• Authors: Eisch, John J.; Liu, Wei; Zhu, Lisheng; Rheingold, Arnold L.
• Is Part Of: European journal of organic chemistry. Issue 33(2014)
• Page Start: 7489
• Page End: 7498
• Publication Date: 2014-10-14
• Subjects: Nitrogen heterocycles -- Cyclic rearrangement -- Electron transfer -- SET oxidation -- SET reduction; Chemistry, Organic -- Periodicals; Organic compounds -- Synthesis -- Periodicals; Bioorganic chemistry -- Periodicals; Chemistry, Physical organic -- Periodicals; 547
• DOI: 10.1002/ejoc.201403101
• Languages: English
• ISSNs: 1434-193X

Abstract

Abstract: In our continuing attempts to convert tub‐shaped dibenzo[1, 4]diazocines or dibenzo[1, 5]diazocines into necessarily planar Hückel aromatic ten‐π‐electron dianions or dihydro derivatives of the central diazocine ring, we have added requisite electrons by Na or Li metal in THF. Subsequent hydrolysis yielded no evidence for the formation of such Hückel aromatic products but in each case a profound rearrangement of the tricyclic diazocine had instead occurred. In the present study we have attempted to form the unknown aromatic 6, 11‐diphenyldibenzo[ b, f ][5, 12]‐dihydro[1, 4]diazocine at 25 °C by such a straightforward addition of two electrons to 6, 11‐diphenyldibenzo[ b, f ][1, 4]diazocine. We were encouraged by the prior reduction of the unsubstituted [1, 4]diazocine to 1, 4‐dihydro‐[1, 4]diazocine, which by X‐ray and 1 H NMR evidence displays aromatic‐like properties. However, this diphenyldibenzo[1, 4]‐diazocine upon reduction underwent instead an unusual, serendipitous rearrangement to yield quantitatively 2‐(2‐aminophenyl)‐1, 3‐diphenylisoindole. Then in a purposive search for other reductants capable of reductively rearranging this [1, 4]diazocine to its corresponding isoindole, we discovered three other reductants, namely o ‐diaminobenzene, titanium(II) salts, and concentrated aqueous hydriodic acid with visible light. Conversely, again in a serendipitous observation, it was found that O2 in CHCl3 with visible light could readily convert the isoindole in an oxidative rearrangement back into the [1, 4]diazocine. A purposive method for achieving this oxidative rearrangement was then found to be treatment with DDQ. General mechanistic pathways are proposed via SET intermediates for both redox interconversions. Abstract : Our attempt to form the aromatic 6, 11‐diphenyldibenzo[ b, f ]5, 12‐dihydro[1, 4]diazocine by treating 6, 11‐diphenyldibenzo[ b, f ][1, 4]diazocine with Na and then water led instead to 2‐(2‐aminophenyl)‐1, 3‐diphenylisoindole. Other reductants for this reaction were o ‐diaminobenzene ( o ‐DAB), titanium(II) salts and HI; the reverse reaction was caused by O2 or DDQ.