8-bromo-2,2 -dimethyl-6-nitro phenyl-

Pyrimidine, 5-benzyl-4,6-dimethyl-2-phenyl-synthesis, 3, 118 Pyrimidine, 2-benzyl-5-nitro-synthesis, 3, 130 Pyrimidine, benzyloxy-pyrimidinone synthesis from, 3, 133 Pyrimidine, 4,5-bis(alkylamino)-synthesis, 3, 121 Pyrimidine, 2-bromo-aminolysis, 3, 100 H NMR, 3, 62 reactions... 

Compounds 4 and 5 would be expected to be inert toward electrophilic substitution, and, in fact, sulfonation of the 2-phenyl derivative 201234 and nitration of the 1-phenyl derivative 202l69b lead to substitution on the phenyl rings. A series of electrophilic substitutions on the product (203) from 1 -(n-butyl)[l,2,3]triazolo[4,5-c]pyridine and dimethyl sulphate give 7-bromo-, 7-nitro-, and 7-chlorotriazolopyridin-4-ones the electrophilic attack may, in each case, be on the triazolopyridinone.169... 

When large groups, such as phenyl, bromo, ethoxycarbonyl or nitro are attached at position 3, the principal products are l-alkylcinnolin-4(l/f)-ones. Cyanoethylation and acetylation of cinnolin-4(l/f)-one takes place exclusively at N-1. Phthalazin-l(2/f)-ones give 2-substituted derivatives on alkylation and acylation. Alkylation of 4-hydroxyphthala2in-l(2/f)-one with an equimolar amount of primary halide in the presence of a base leads to 2-alkyl-4-hydroxyphthalazin-l(2/f)-one and further alkylation results in the formation of 4-alkoxy-2-alkylphthalazinone. Methylation of 4-hydroxy-2-methyl-phthalazinone with dimethyl sulfate in aqueous alkali gives a mixture of 4-methoxy-2-methylphthalazin-l(2/f)-one and 2,3-dimethylphthalazine-l,4(2//,3//)-dione, whereas methylation of 4-methoxyphthalazin-l(2/f)-one under similar conditions affords only 4-methoxy-2-methylphthalazinone. 

Groups of reportedly photochromic systems which deserve further study include (a) disulfoxides (123,124), (b) hydrazones (125-129), (c) osazones (130-133), (d ) semicarbazones (134-143), (e) stilbene derivatives (144), (/) succinic anhydrides (145-148), and (g) various dyes (149,150). A number of individual compounds also remain unclassified as to their mechanism of photochromic activity. These include o-nitro-benzylidine isonicotinic acid hydrazide (151), 2,3-epoxy-2-ethyl-3-phenyl-1-indanone (152), p-diethyl- and p-dimethyl-aminophenyli-minocamphor (153), brucine salts of bromo- and chloro-nitromethionic acid (154), diphenacyldiphenylmethane (155,156), 2,4,4,6-tetraphenyl-1,4,-dihydropyridine (155,156), 2,4,4,6-3,5-dibenzoyltetrahydropyran (155,156), o-nitrobenzylidenedesoxybenzoin (157), p-nitrobenzylidene-desoxybenzoin (157), N-(3-pyridyl)sydnone (158,159), tetrabenzoyl-ethylene (160), and the oxidation product of 2,4,5-triphenylimidazole (161,162). 

Exposure of the 8-bromo-2,2 -dimethyl-6-nitro-l -phenyl-(2H-[l]benzospiro-pyran-2,2 -indoline) to light causes it to isomerize into the coloured form. In a solvent it rapidly converts to the bleached form and exhibits first-order kinetics.The process is thermally activated and will require volume for the relative rotation of the two parts of the molecule to effect ring closure. However, if the same process is carried out with the dye in a polymer matrix the process now depends on there free volume available for the rotation of the molecule required for ring closure to occur. Studies of the kinetics (Figure 7.15) indicate that simple kinetics is no longer followed and that a more complex analysis is required. Good fits of the data can be obtained if it is assumed that the process is split into two processes. The initial fast decay is essentially the same as that seen in a liquid and indicates that the ring closure process is only subject to thermal control. This implies that these molecules have sufficient free volume available to execute the process. 

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