2-Amino-l-aryl

A convenient route to 4-aryl-1,3-dithiolylium salts (48) is the treatment of 2-amino-4-aryl-l,3-dithioles (153) with acids in ethanol solution. Yields of (48) are generally higher than 90% <80AHC(27)151>. 

A similar and convenient route to 2-unsubstituted-4-aryl-1,3-dithiolium salts (122) is by the action of acids in ethanol upon 2-amino-4-aryl-l,3-dithioles (121). Yields are generally higher than 90%. °... 

This was later extended to the synthesis of novel pyrimido[l,3-a]pyrimidines under solvent-free conditions. Ethyl 2-amino-4-aryl-l,4-dihydro-6-phenylpyrimi-dine-5-carboxylates reacted regioselectively with 3-formylchromone or diethyl (ethoxymethylene)malonate, without solvent, to afford pyrimido[l,3-a]pyrimidines (Scheme 10.107) [211]. 

Habermann, J., Ley, S.V., Scicinski, J.J. et al. (1999) Clean synthesis of a-bromo ketones and their utilization in the synthesis of 2-aIkoxy-2,3-dihydro-2-aryl-l,4-henzodioxanes, 2-amino-4-aryl-l,3-thiazoles and piperidino-2-amino-l,3-thiazoles using polymer-supported reagents. Journal of the Chemical Society - Perkin Transactions 1, 2425-2427. 

Amino-4-aryl-selenazole-5-acetic acids were used by Knott for the preparation of naphtho-l, 2, 4,5-selenazoles. " ... 

Amino-4-aryl-5-acetic acid selenazoles were used by Knott (2)i as intermediates in the preparation of l .2, 4.5-naphthoselenazoles (21. 30. 31). 

Aroylformamido-4-aryl-l,2,5-thiadiazoles 120 on treatment with MCPBA in chloroform at reflux afford 3-amino-4-aryl-l,2,5-thiadiazoles 121 (Scheme 18), but in the presence of ethanol the 3-ethoxycarbamoyl-4-aryl-l,2,5-thiadiazole 122 was also isolated <1999JHC515>. A-Aroylation could readily be achieved to give thiadiazoles 123 using the acid chloride in chloroform at room temperature. 

The reaction of the trichloromethylarenes 146 with thiosemicarbazide 138 in a boiling methanol-pyridine mixture afforded the 2-amino-5-aryl-l,3,4-thiadiazoles, while under similar conditions trichloromethylarenes 146 were converted to the diaryl-1,3,4-thiadiazoles with thiobenzhydrazide 147 (Equation 52, Table 7) <1996RCB1185>. 

The reaction of 2-amino-5-aryl-l,3,4-oxadiazoles 449 with chloroacetic acid afford imidazo[2,l- ][l,3,4]oxadiazoles 450 (unreported yield) (Equation 101) <1996JIC702>. 

Alkylation of 2-amino-5-(alkyl, aryl, hetaryl)-l,3,4-oxadiazoles is said to occur at the ring N atom (N-3) (94HOU526), but this report remains doubtful. In addition, as others have pointed out, the very low basicity of imidazo[2,l-b][l,3,4]oxadiazoles precludes the isolation of hydrohalides of type 20. 2,6-Diaryl-imidazo[2,l-ft][l,3,4]oxadiazoles 22 can be obtained directly by treatment of 2-amino-5-aryl-l,3,4-oxadiazoles 21 with phenacyl-bromides in ethanol [reflux in a water bath at 70°C ( ) for 5 h] (84MI1). 

Amino-5-aryl-l,3,4-thiadiazole was treated with thionyl chloride in dry benzene to yield the N-sulfinylamine (93) an unstable compound, characterized by NMR and further derivatization. The sulfinylamine moiety caused an upheld shift on C(2) (4 6 ppm) comparable to a carbonyl or sulfonyl group, indicating the double-bond character of the N—S bond. Reaction of (93) with 2,3-dimethylbuta-1,3-diene yielded (94) via thermal cycloaddition <89JCS(P2)i855>. 

Alkyl-2-ainino- bzw. 2-Amino-5-aryl-l,3,4-oxadiazole allgemeine Arbeitsvorschrift234 41S Man lost das Kohlensaure-(2-acyl-hydrazid)-amid in siedendem Phosphoroxichlorid und erhitzt 1 -3 h unter RiickfluB. Die abgekiihlte Losung wird langsam zu Eiswasser gegeben. 

Ein haufig praktiziertes Verfahren ist die oxidative Cyclisierung mit Iod/Kaliumiodid443,446 453. Auch mit Brom in Chloroform446 wurden gute Ausbeuten an 2-Amino-5-aryl-l,3,4-oxa-diazolen erreicht. 

Die Amino-Gruppe von 2-Amino-5-aryl-l,3,4-oxadiazolen la6t sich nitrosieren428 651. Die hohe Aciditat der 5-Aryl-2-nitrosamino-l,3,4-oxadiazole erlaubt eine Reinigung durch Ex-traktion mit Basen und Fallen mit Saure. 

Reactions of a number of l-phenylimidazole-2-carboxamides with chlorine in acetic acid, NCS, or hypochlorite failed to introduce chlorine into the 4- or 5-positions (80JHC409). Chlorination of a variety of 2,4-disubstituted imidazoles, however, was quite facile, Thus, 2,4-diesters [83JCS(P1)809] and 2-amino-4-aryl compounds [80IJC(B)526] were readily 5-chlorinated, and even when both the 4- and the 5-positions were blocked, as in 5-aminoimidazole-4-carboxamide, 2-chlorination with iodine monochloride was possible (89MI5). When all three carbons were substituted (e.g., in 2,4,5-triphenyl-, 2-chloro-4,5-diphenyl-, and 2-trichloromethyl-... 

Cyclocondensation of 6-methylthio-5-cyano-l,2,3,4-tetrahydropyridine-2,4-dione with arylidenemalononitrile (174) in the presence of piperidine in boiling ethanol gave 2-amino-4-aryl-6-methylthio-8-oxo-4,8-dihydropyr-ido[2,l-h][l,3]oxazine-3,7-dicarbonitrile (175) (92MI4). 

Amino-5-aryl-l,3,4-oxadiazoles form stable N-nitrosamines (71c) which are converted into hydrazines (7ld) with zinc in acetic acid. Treatment of the hydrazine (71d) with nitrous acid yields the corresponding azide and with benzaldehyde a hydrazone is formed (B-61MI42300). On heating in benzene or in nitrobenzene, the nitrosamine (71c) undergoes the Gomberg-Bachmann reaction to yield 2,5-diaryl-l,3,4-oxadiazoles (73JCS(P1)1357). 

There are some literature reports on the reactions of 1,2,4-triazoles. 2-Amino-4-aryl-5-( I //-l, 2,4-triazol-1 -yl)thiazolc derivatives were synthesized from the reaction of a-bromo substituted acetophenone and thiourea <07SC199>. 5-Amino-l-methyl-l//-[l,2,4]triazole-3-carboxylic acid were employed as precursors in peptide synthesis <07SC1917>. 3-... 

Acylamino-l,3,4-thiadiazoles have been reduced with lithium aluminium hydride to the corresponding 2-alkylamino derivatives. 2-Amino-5-aryl-l,3,4-thiadiazoles have been found to undergo the Mannich reaction with a variety of methylene compounds. ... 

Substituent effects on the polarographic reduction of l-amino-4-aryl-l,2,3-triazoles and l//-4-aryl-l,2,3-triazoles of the general formula (67) have been reported. Cathodic halfwave potentials E1/2) determined in acetonitrile at 20 °C were between -2.1 and -2.6 V. Linear relations were found between E1/2 and the tt-electron density at C-5, as well as Hammett [Pg.689]

Ultraviolet spectra of 2-aryl-I,3-dithiolium-4-olates have been measured. The longest wavelength band is found at 508 nm in the 5-methyl-2-phenyl derivative.In 2,5-diaryl derivatives the maximum falls in the range 533-599 nm and is attributed to a tc - tc transition. In the 2-amino-5-aryl-l,3-dithiolium-4-olates, a band between 456 and 485 nm is similarly assigned. 

---