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Selenoamides

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. [Pg.219]

The difficulties posed by the synthesis of 2-alkyl and 2-arylselenazoIes substituted in the 4- and 5-positions arise mainly from the preparation of the intermediates, especially the selenoamides. [Pg.220]

The replacement of selenoamide by selenourea in the Hantzsch s synthesis. (1st method) leads to 2-aminoselenazoles 2, 14. 15). This series of compounds has been well developed, mainlv because selenourea is much more easily accessible than the selenoamides, but also because a wide variety of a-halogenated carbonyl compounds are available for the Hantzsch s evdization reaction (Scheme 5). 2-Aminoselenazole itself was prepared from commercially available chloroacetaldehyde semihydrate... [Pg.222]

If in the Hantzsch s synthesis, selenoamide is replaced by a selenosemi-carbazide (HjJN -NH-CSe-l ). condensation can take place upon... [Pg.232]

PyrryH-selenazoles (Scheme 23). obtained by condensation of 2-chloroacetylpyrrole with selenoamides, are also used in dye chemistry (371. [Pg.236]

The general formula of the 2-(2- or 4-furyl. thienyl, or selenienyljselenazoles is shown in Scheme 24 (40, 105. 106). (Selenienyl-2), (furyl-2), (thienyl-2), and (chloromethyi-4)selenazoles may be prepared by Hantzsch s reaction from selenoamides as described in Scheme 25. Hydrolysis give hydroxymethyl derivatives. [Pg.237]

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%,... [Pg.345]

In two patents,the preparation of thioether-substituted selena-zoles of the general formula (6) have been described. These are stated to be formed by reaction of halogenoketothioethers with selenoamide components selenoacetamide, selenobenzamide, and A -ethylseleno-urea are given as examples. The resulting selenazoles were not further characterized. They are stated to be starting materials for the preparation of cyanine dyestuffs which are useful photographically. [Pg.353]

Pyrryl)selenazole is protected for the same purpose, by another patent. This is stated to be prepared from 2-chloroacetyl-pyrrole with selenoamides by analogy with the corresponding thiazole. No concrete example of the reaction is given. [Pg.353]

Furyl)selenoamide, reaction witha-ehioro-Q-ethoxalyi acetate, 237... [Pg.149]

Thienyl)selenoamide, reaction with a-chloro-Q-ethoxalylacetate, 237... [Pg.153]

Selenienvl) selenoamide reaction with u-chloro-o-ethoxalyl acetate,... [Pg.334]

Amides such as DMF or ureas such as N,N-tetramethylurea react with bis(trimethylsilyl)selenide 604 in the presence of BF3-OEt2 to give selenoamides, for example 617, or selenoureas whereas esters such as n-butyl benzoate react with 604 in the presence of Bp3-Et20 and 2,3-dimethylbutadiene to give 619 via 618 [157]. On heating with P4Sio/sulfur and hexamethyldisiloxane 7 y9-ketoesters such as ethyl acetoacetate are converted to 3H-l,2-dithiole-3-thiones such as 620 in high yields [158] (Scheme 5.51 cf. also Section 8.6). [Pg.110]

Reports regarding selenoamides and selenoureas are less than the corresponding thioamides, thioureas, amides and ureas because of instability of compounds including selenium atom and their difficulty in the preparation. Recently, preparation methods to overcome some difficulties have been developed. Their reactions, preparation, application to heterocycles or biological assay systems have been actively investigated. [Pg.177]

Primary selenoamides are prepared by reaction of nitriles with appropriate selenating reagent, such as phosphorus (V) selenide (P2Se5), hydrogen selenide (H2Se), Al2Se3, NaSeH, trw(trimethylsilyl)monoselenophosphate or potassium selenobenzoate (Scheme 81).248 252... [Pg.178]

For the preparation of secondary and tertiary selenoamides, several methods have been used reaction of lithium alkyneselenolates (obtained using metallic selenium) with amines, aromatic diselenoic acid Se-methyl esters with amines or dihalomethane with elemental selenium, NaH and amines (Scheme 83).258 266... [Pg.179]

Selenoureas are prepared by reaction of isoselenocyanates with amines, or by reaction of carbodiimides with a mixture of LiAlH4/Se and by reaction of cyanamides with LiAlH4/Se.267 272 The tyrosinase inhibitory activity and superoxide radical scavenger effect of selenoamides and selenoureas have been investigated (Scheme 84).273 275... [Pg.180]

Selenazole and selenazine derivatives are obtained by reaction of selenoamide or selenourea with nucleophiles.276... [Pg.180]

Reactions of primary selenoamides with a-haloketones, haloacyl halides or ketones provides 1,3-selenazole derivatives (Scheme 85).277 283... [Pg.180]

The solid complex of TV-methylbenzothiazol -2(3H)-selcnonc (mbts) with Te(Ph)Br contains two symmetry-independent molecules, both of which pack in a way that weak dimers through T-T contacts are formed (Figure 29). In molecule A the distance between the Te atom and the neighbouring conjugated ji-system is 365.6 pm, and the Te atom is positioned over the central carbon atom of selenoamide function (Te- Se 413.8 Te- -S 396.1 Te- -N 393.4 pm). In molecule B, the distance from Te to the rc-system is 370.5 pm, and the Te atom is shifted away from the central carbon atom towards the endocyclic sulfur atom (Te- -Se 422.7 Te- -S 390.6 Te- -N 450.2 pm). Related T-T contacts are a general kind of packing for Se and Te-centred T-structures. [Pg.855]


See other pages where Selenoamides is mentioned: [Pg.237]    [Pg.346]    [Pg.350]    [Pg.179]    [Pg.186]    [Pg.79]    [Pg.145]    [Pg.177]    [Pg.178]    [Pg.178]    [Pg.180]    [Pg.180]   
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