1.3- Selenazoles synthesis

Benzoxepin-4-carbaldehyde, dihydro-from chromones, 3, 713 Benzoxepin-4(3H)-one from isochromanone, 3, 726 [l]Benzoxepino[3,4-d]selenazoles synthesis, 6, 345 Benzoxepins... 

Benzo[c]thiepin-5-one, 4,5,6,7-tetrahydro-synthesis, 4, 823, 7, 585 [ 1 ]Benzothi epino[3,4-d ]selenazoles synthesis, 6, 345 Benzothi epins... 

Pyrrolo[3,4-6]quinoxaline, 2-/-butyl-l,3-dihydro-oxidation, 4, 509 Pyrrolo[3,2-d ]selenazoles synthesis, 6, 344, 1009... 

In the first chapter, devoted to thiazole itself, specific emphasis has been given to the structure and mechanistic aspects of the reactivity of the molecule most of the theoretical methods and physical techniques available to date have been applied in the study of thiazole and its derivatives, and the results are discussed in detail The chapter devoted to methods of synthesis is especially detailed and traces the way for the preparation of any monocyclic thiazole derivative. Three chapters concern the non-tautomeric functional derivatives, and two are devoted to amino-, hydroxy- and mercaptothiazoles these chapters constitute the core of the book. All discussion of chemical properties is complemented by tables in which all the known derivatives are inventoried and characterized by their usual physical properties. This information should be of particular value to organic chemists in identifying natural or Synthetic thiazoles. Two brief chapters concern mesoionic thiazoles and selenazoles. Finally, an important chapter is devoted to cyanine dyes derived from thiazolium salts, completing some classical reviews on the subject and discussing recent developments in the studies of the reaction mechanisms involved in their synthesis. 

This chapter is an attempt to present the important results of studies of the synthesis, reactivity, and physicochemical properties of this series of compounds. The subject was surveyed by Bulka (3) in 1963 and by Klayman and Gunther (4) in 1973. Unlike the oxazoles and thiazoles. there are few convenient preparative routes to the selenazoles. Furthermore, the selenium intermediates are difficult to synthesize and are often extremely toxic selenoamides tend to decompose rapidly depositing metallic selenium. This inconvenience can be alleviated by choice of suitable reaction conditions. Finally, the use of selenium compounds in preparative reactions is often complicated by the fragility of the cycle and the deposition of metallic selenium. 

The comparatively ready accessibility of selenocarboxamides has encouraged the use of this procedure for the synthesis of selenazoles (1889LA(250)294). Reaction of the a-chloro-carbonyl compound (73) with the selenocarboxamide (74) provided a ready synthesis of a variety of substituted selenazoles (75). Useful variations of this general procedure are described in detail in Chapter 4.20, and particularly attractive is the reaction of hydrogen selenide with a mixture of a nitrile and the a-halogenoketone to afford the selenazole (48YZ191, 79S66). 

Alanine, ( )- -(2-amino-1,3-selenazol-4-yl)-synthesis, 6, 343 Alanine, phenyl-p-hydroxylation, 7, 565 Alanine, selenienyl-synthesis, 4, 964 Alanine, y3-2-selenienyl-applications, 4, 970 Alanine, y3-3-selenienyl-applications, 4, 970 Alanine, y3-2-thienyl-biological activity, 4, 911 Alanine, -3-thienyl-biological activity, 4, 912 L-Alanine, y-L-glutamyl-y3-pyrazolyl-occurrence, 5, 303 L-Alanine, -pyrazolyl-occurrence, 5, 303 Alanine raeemase inhibition, 1, 266 Albendazole... 

Selenazole, 2-acetamido-nitration, 6, 341 Selenazole, 2-alkyl-nitration, 6, 340 Selenazole, 2-amino-bromination, 6, 341 sulfonation, 6, 341 synthesis, 6, 342... 

Selenazol-2-inium bromide, 2-amino-X-ray diffraction, 6, 339 Selenazolin-4-ones synthesis, 6, 345... 

Thieno[3,2-d]selenazole, 2-methyl-synthesis, 6, 344 Thienoseleninium salts, 4, 1029 Thienoselenophenes NMR, 4, 13... 

The difficulties encountered in the synthesis of 2-alkyl- and 2-aryl-substituted selenazoles lie principally in the preparation of the corresponding selenoamides. In this respect, a method is worthy of note in which the use of selenoamides is dispensed with. For this, a nitrile, a hydrogen selenide, and an a-halogenoketone are reacted together in the presence of a condensation catalyst. Phosphorus oxychloride, alone or mixed with zinc chloride or phosphorus trichloride, is specially suitable. The yields of the corresponding 2-alkylseIenazoles are up to a maximum of 25%,... 

A variation of the general method for the synthesis of 2-amino-selenazoles is to avoid the use of the free a-halogenocarbonyl compound and in its place react the corresponding ketone and iodine with selenourea.This procedure is also taken from thiazole chemistry. By contrast with thiourea, the reaction with selenourea needs a longer reaction time and the work up of the reaction mixture is somewhat more difficult. Usually an excess of the ketone is used. In the preparation of 2-amino-4-( n-nitrophenyl)selenazole, a very high yield, calculated on the amount of iodine used, was obtained. To explain this peculiar result, the oxidative action of the nitro group was invoked. This liberates free iodine from some of the hydrogen iodide eliminated in the condensation reaction, and the free iodine then re-enters into the reaction. 

With the synthesis of the benzylidene hydrazones of selenazoles, it was possible to prepare formazans containing a selenazole ring. Of the compounds already described (Section I,C,1), 2-benzylidene-hydrazino-4,5-diphenyl- and 2-benzylidenehydrazino-4-methyl-5-carb-ethoxy-selenazole were used to couple with diazonium salts in order... 

The preparation of the selenazolyl-pyrazolones was then effected by a second method, in which first the pyrazolone ring and afterward the selenazole ring was formed. For this purpose -ketoester seleno-semicarbazones were first converted to the corresponding 1-seleno-carbamoyl-3-aIkylpyrazol-5-one. These, by condensation with a-halo-genocarbonyl compounds according to the Hantzsch synthesis, formed the selenazole ring as a second step (17). 

The difficulties posed by the synthesis of 2-alkvl and 2-ary selenazoles substituted in the 4- and 5-positions arise mainly from the preparation of the intermediates, especially the selenoamides. 

Diethoxymethylacetate, in synthesis of, trimethine thiazolocyanines, 55 2-Diethylamino-4-methyl-5-nitro selenazole. melting point, 243... 

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