Pyrazolo pyrimidines rearrangements

Diazopyrrole 196 with diethyl acetylenedicarboxylate gives the spiro compound 197. Rearrangement of 197 gives the pyrazolo[l,5-c]pyrimidine 198 (74LA1550). 

Pyrazolo[l,5-a]pyrimidin-7-ones 220 rearrange on treatment with sodium hydroxide into the pyrazolo[3,4-fc]pyridines 221 (77USP4048184). 

The presence or absence of the dioxolane protecting group in dienes dictates whether they participate in normal or inverse-electron-demand Diels-Alder reactions.257 The intramolecular inverse-electron-demand Diels-Alder cycloaddition of 1,2,4-triazines tethered with imidazoles produce tetrahydro-l,5-naphthyridines following the loss of N2 and CH3CN.258 The inverse-electron-demand Diels-Alder reaction of 4,6-dinitrobenzofuroxan (137) with ethyl vinyl ether yields two diastereoisomeric dihydrooxazine /V-oxide adducts (138) and (139) together with a bis(dihydrooxazine A -oxide) product (140) in die presence of excess ethyl vinyl ether (Scheme 52).259 The inverse-electron-demand Diels-Alder reaction of 2,4,6-tris(ethoxycarbonyl)-l,3,5-triazine with 5-aminopyrazoles provides a one-step synthesis of pyrazolo[3,4-djpyrimidines.260 The intermolecular inverse-electron-demand Diels-Alder reactions of trialkyl l,2,4-triazine-4,5,6-tricarboxylates with protected 2-aminoimidazole produced li/-imidazo[4,5-c]pyridines and die rearranged 3//-pyrido[3,2-[Pg.460]

Ring opening of 3-(phenylsulfonyloxy)pyrido[3,4-d]pyrimidine-2,4-dione (587) with sodium methoxide, followed by a Lossen rearrangement gave the hydrazinopyridine ester (588) which in refluxing acid yielded 1 //-pyrazolo[3,4-c]pyridin-3-one (589) (Scheme 75) <74JHC163>. 

Using the general method described in Section 7.08.10.2 <74JHC163> 3-(phenylsulfonyloxy) pyrido[4,3-fi ]pyrimidine-2,4-dione (590) ring opens with sodium methoxide and rearranges to a hydrazinopyridine ester, which in refluxing acid yields l//-pyrazolo[4,3-c]pyridin-3-one (591) (Equation (59)). 

A 5-alkoxypyridoL4,3-4]pyrimidin-4(3f/)-one has been synthesized via a selective A-oxidation followed by a regioselective Meisenheimer A-oxide rearrangement <04TL3737>. 1,2,3,4,5,6,7,8-Octahydroquinazolinediones and 3,4-dihydro-l/f-indeno l,2-rf]pyrimidine-2,5-diones were obtained by a modified Biginelli synthetic route <041JC135>. A series of l//-pyrazolo[3,4-af -... 

Laurina and co-workers used the Dimroth rearrangement in their synthesis of novel pyrazolo[3,4-i/][l,2,3]triazolo[l,5-l]pyrimidine systems. These compounds have the potential to serve as DNA intercalators in a similar fashion to acridines, anthracyclines, and actinomycins. Treatment of compounds 61, 63 and 65 with refluxing sodium ethoxide in ethanol gave the corresponding Dimroth products 62, 64 and 66 in high yield. 

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