Dimethyl di

Methyl o-nitrobenzyl ketoxime 2,5-Dimethyl-3,6-di(o-nitrophenyl)-3,6- dihydro 294,297... 

Nitration of 2,5-dimethyl-3,6-diphenylpyrazine with nitric-sulfuric acid occurs in the benzene rings to give 2,5-dimethyl-3,6-di-m-nitrophenylpyrazine (191). 

In another approaeh [88IJC(B)570], reaetion of 2-mereapto-4,5-di-p-tol-ylimidazole 43 with a-halo carboxylie acids enabled the synthesis of several imidazo[2,l-h]thiazoles. Acylative ring closure of 4,5-di-p-tolylimidazo-2-thioacetic acid (44, R = H) or 2-thiopropionic acid (44, R = Me) provides 5,6-di-p-tolylimidazo[2,l-h]thiazole-3(2//)-one (45, R = H) or its 2-methyl analog (45, R = Me). The synthesis of annelated imidazo[2,l-h]thiazoles (e.g., 46) can be achieved in one step by reaction of 2,3-dichloroquinoxaline with 43. The intramolecular eyelization of l-vinylimidazole-2-thiones to 2,5-dimethyl-3,6-arylimidazo[2,l-h]thiazoles with excellent yield has been reported (93T6619). 

Interestingly, this result contrasts with the reported photooxygenation of acyclic 1,3-dienes46. For example, 2-methyl-l,3-pentadiene leads to the Diels-Alder product, 3,5-dimethyl-3,6-di-hydro-1,2-dioxin, in 58% yield462. 

Ethyl 3-ethoxy-a-nitroacrylate with 1,1-diphenylhydrazine in ethanol followed by heating has been shown to give l,4-bis(diphenylamino)-2,5-diethoxycarbonyl-l,4-dihydropyrazine (1586). A small amount of 2,5-dicyano-l,4-bis(dimethylamino)-1,4-dihydropyrazine was obtained from the reaction of 2-chloro-3-(2, 2-dimethyl-hydrazino)propionitrile [(Me)2NNHCH2CH(Cl)CN] with sodium hydride (1587). Hexaalkyl-l,4-dihydropyrazines and other 1,4-dialkyl-1,4-dihydropyrazines can be obtained by thermolysis of the products of reaction of a-(alkylamino)carboxylic acid esters with alkylmagnesium bromide. Thus the reaction of ethyl a-s-butyl-aminopropionate with ethylmapesium bromide, followed by heating in vacuo to 250-300°, gave 2,5-dimethyl-3,6-diethyl-l,4-di-s-butyl-l,4-dihydropyrazine (1588). 

Anhydro-l,6-di-0-tosyl-L-iditol, A-654 2,5 Anhydro-3,6-di-0-tosyl-L-idose dimethyl dithioacetal, A-657 2,5 Anhydro-3,4-di-0-tosyl-D-lyxose dimethyl acetal, A-665 2,5 Anhydro-3,4-di-0-tosyl-L-lyxose dimethyl acetal, A-665... 

Characteristic absorption bands of the various structural forms of the 1,3-thiazines are known <1996CHEC-II(6)383>. An interesting photochromic behavior of 4-heteroaryl-5,6-di(2,5-dimethyl-3-thienyl)-2-phenyl-4f/-l,3-thiazines 54 was observed on irradiation of the colorless compounds (Figure 2). The resulting tetracyclic compounds 55 are colored <2005CHE86>. 

A series of 4-heteroaryl-5,6-di(2,5-dimethyl-3-thienyl)-2-phenyM//-l,6-thiazines 54 with photochromic properties was prepared by reacting 3-(2-(2,5-dimethylthiophen-3-yl)ethynyl)-2,5-di ethylthiophene with thiobenzamide and aldehydes <2005CHE86, 2005PS1503>. The acid-catalyzed cyclocondensation of cyclopentanone, aromatic aldehydes, ArCHO, and thiourea affords the cyclopenta[t ]l,3-thiazines 37 <2006PS1655>. Two equivalents of the aldehyde are required. The same products are isolated when 2,5-dibenzylidenecyclopentanones are treated with thiourea under the same conditions. 2-Amino-4i/-l,3-thiazines 184 are easily synthesized in one pot by the reaction of aromatic alkynes, R feCH, aromatic aldehydes, R CHO, and thiourea in the presence of TFA/acetic acid <2005OL3797>. 

The number of 1,2,4,5-tetrazines used in these cycloaddition reactions is limited. The most frequently used are the 3,6-dicarboxylates, the 3,6-diphenyl, 3,6-dimethyl, 3,6-di(2-pyridyl) and bis(perfluoroalkyl) compounds a few others have also been used. The most reactive substances seem to be the 1,2,4,5-tetrazinedicarboxylates, possessing the extra electron-withdrawing effect of the two carboxylate groups. 

Alkaline hydrolysis of the di-A-oxide of 2,5-dichloro-3,6-dimethyl-pyrazine (215) readily yields the monohydroxamic acid (216), but the second chlorine atom is inert. Both chlorine atoms in compound 215 may be displaced by ethoxide or benzyloxide ion. Acid treatment of the dibenzyloxy-1,4-dioxide (217) yields compound 218 which with... 

Dibenzylidene-l,4-dimethyl-3,6-dihydro-2,5(1//,4//)-pyrazinedione (285) gave 3-benzylidene-6-(a-bromobenzyl)-6-hydroxy-l,4-dimethyl-l,4-dimethyl-3,6-di-hydro-2,5(l//, 4//)-pyrazinedionc (286) [NBS/H20—dioxane (— HOBr), 20°C, 12 h erythro and threo isomer, 50 and 33%, respectively, after separation],1030 also analogous reactions.1036... 

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