Phthalazine 1.4- dione, cycloaddition

Similarly, a mixture of stereoisomers (47% yield fija 80 20) is obtained in the cycloaddition of phthalazine-l,4-dione (generated in situ) to vitamin D3n, the configuration of the diastereomers was assigned by analogy with the previously reported triazole adducts. 

Diels-Alder cycloaddition with, for example, butadiene <85JOC5604>. 7V-Bromosuccinimide can be used to oxidise the initial adduct formed between phthalazine-l,4-dione and 1,4-diphenyl butadiene via benzylic bromination and thermal elimination of hydrogen bromide the intermediate bromide is, however, very labile towards nucleophiles, and base causes cleavage of the phthaloyl residue, leaving 3,6-diphenylpyridazine <86JOC3123>. 

The reactivity of pyridazines in Pd-catalyzed reactions was of interest. For example, the Heck alkenylation at C5 of 6-phenyl-3(2//)-pyridazinones was investigated, with the aim of suppressing production of 4-phenyl-6-substituted-2-phthalazinone byproducts <04TL3459>. In another study, the reactivity of 5-iodopyridazin-3(2f/)-ones in Pd-catalyzed reactions was investigated to develop an efficient route to 2,5-disubstituted pyridazin-3(2/f)-ones <04T12177>. Other pyridazine syntheses relied on condensation approaches. Benzo[g]pyridazino[l,2-i>]-phthalazine-6,13-diones 16 and 17 related to certain anthracyclinones were obtained by cycloaddition of 1,3-dienes to benzo[g]phthalazine-l,4-dione <04H(63)1299>, and pyridazine C-nucleosides synthesized by 14-i-2 cyclocondensation of alkynyl C-nucleosides with substituted tetrazines afforded, upon extrusion of a nitrogen atom, pyrrole C-nucleosides in good yields... 

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