Pyrimidines manganese dioxide

The pyrimidine synthesis was therefore changed to the alkynyl ketone route as the appropriate precursors could be formed under much milder conditions. Thus, treatment of the chloro aldehyde 1002 with ethynyl Grignards or lithium species at low temperature, followed by mild oxidation with manganese dioxide, gave the desired chloro alkynyl ketones 1003, which could be successfully converted to the pyrimidine products 1004, by condensation with substituted guanidines, without displacement of the chlorine atom <2003X9001, 2005BMC5346>. 

Synthesis of the pyrazino[2,1 -bjquinazoline (557) was achieved by oxidative cyclization of the l-(2-aminobenzyl)-4-methylpiperazine (556) with manganese dioxide [68JCS(C)1722], the pyrimidine ring of 557 was formed during this synthesis. The pyrimidine ring of 559 was also formed upon cyclocondensation of anthranilic acids with the cyclic imidate ester (558), followed by removal of the protective group (66USP3280117). 

Oxidative cyclization of the 4-(2-aminobenzyl)-l,4-oxazine (576) with manganese dioxide gave the 1,4-oxazino[3,4-6]quinazoline (577) through the formation of its pyrimidine ring [68JCS(C)1722]. Cyclocondensation of anthranilic acids with the thioimidate ester (578) gave 3,4-dihydro-l,4-oxazino[3,4-6]quinazolin-6(l/f)-ones (579) [791JC(B) 107]. 

The oxadiazolopyrimidine 1-oxide (164) is attacked by nucleophiles at position 7 of the pyrimidine ring and not, as expected, in the oxadiazolo-ring. Oxidation of the covalent adduct (165), obtained by addition of water, with lead tetra-acetate and then with manganese dioxide yields the dinitro-pyrimidinone (166) (Scheme 81). ... 

In an efficient microwave-assisted solution or solid-phase protocol (07Mn2) for 2-amino-4-arylpyrimidine-5-carboxylate derivatives (Scheme 27), 22 (X = S, R = H) was S-alkylated with methyl iodide to 2-methylthiodihydropyrimidines 34, which was sequentially oxidized first with manganese dioxide and then with Oxone to 2-methylsulfonyl-pyr-imidines 66 as precursors of 2-substituted pyrimidines 67 via displacement of the reactive sulfonyl group with N, O, S, and C nucleophiles (Scheme 27). However, direct displacement of the S-methyl group of 34 with nitrogen nucleophiles provided 2-amino-l,4-dihydropyrimidines 68. 

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