Thermal rearrangements, isoquinoline

The precursor 514 has been shown to undergo anodic oxidation to produce the 5-amino-l,2-thiazolium salt 515, which rearranged to the pyrrole 516 upon treatment with triethylamine (Scheme 68) <1995JPR310>. The mechanistic aspects of this approach have also been discussed <1996J(P1)2339>. Cycloaddition of nitrones with acetylenes has been used to generate A -isoxazolines, which underwent thermal rearrangement to pyrroles fused to the isoquinoline framework <1996T12049>. 

JA6181). Thermal rearrangement of diazidoquinones to 2-aza-3-cyano-quinones opened a new, general route to azaquinones and the reaction was elaborated also in the naphthoquinone series to give isoquinoline-1,4-diones (75JA6181). 

Aromatic isoquinolones can be obtained by the thermal rearrangement of isoquinoline iV-oxides thus it was possible to derive the isoquinoline 3 from the iV-oxide 2. Compound 3 could be further functionalized through bromina-tion and subsequent treatment with a mixture of cuprous cyanide and sodium cyanide. ... 

Thus, cycloprop [c] isoquinolines 101 obtained by a stereo specific 1,1-cycloaddition of nitrile ylides 100 undergo two distinct thermal (80 °C) rearrangements depending on the substituents in the cyclopropane ring (equations 35 and 36)52. 

For example, 2-quinolylnitrene rearranges thermally to 1-isoquinolyl-nitrene, from which the products 166a-c arise (Scheme 33) 221,222,222a cyclic carbodiimide 165 (R = H) was isolable at - 196°C and directly observable by IR spectroscopy (2000 cm following flash vacuum pyrolysis of either tetrazolo[ 1,5-a] quinoline or tetrazolo [5,1-a] isoquinoline at 490°C. Compound 165 dimerized on warming to — 55°C. This intermediate had originally been postulated as the mesomeric form 165a (Scheme 33). The bicyclic azirines 167 and 168 (Scheme 33) can be written as intermediates or transition states en route to 165, but they are not expected to be stable intermediates under these reaction conditions, and no evidence for their formation has been obtained. 

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