1.2.4.5- Tetrazines furan synthesis using

A new potential synthesis of anthraquinones based on l-acetoxybenzo[c]furan (470) has been reported. The s-tetrazine reaction used to generate the benzo[c]furan proceeded in the presence of N-methylmaleimide to give the expected adduct (471). The reaction takes a different path in the presence of quinones to yield a novel phthalide (472), the structure of which was confirmed by X-ray diffraction (81AJC1223). 

A broadly applicable synthesis of benzol/-]furans by Warrener relies on DielsAlder/retro DielsAlder reactions with s-tetrazines. Using this methodology with 3,6-di(pyridin-2-yl)-i -tetrazine 162 the generation of an isolable 5,6-(bistri-methylsilyl)benzo[c]furan 163 has been achieved (Scheme 97) <2002T9413, CHEC-III(3.07.6)551>. 

Inverse demand Diels-Alder reactions of tetrazines 1 to psoralenes 267 were reported to furnish tetracyclic pyridazine dicarboxylates 268, which were used as the key intermediates in the synthesis of nitrogenated isosteres of potent DNA inhibitors <2003T8171>. In some cases, cycloaddition was followed by opening of the furan ring to give pyridazinyl-substituted coumarins 271 (Scheme 66) <2000JHC907, 2003SL2225>. 

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