Selenocarboxamides

Alkyl or arylhexahydrobenzoselenazoles (Scheme 4) are synthesized by reaction of a-ch orocyc ohexylamine with selenocarboxamides (10). 

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). 

Hantzsch s synthesis, 229 Alkyl group, in the chain of monomethine dyes, influence on absorption, 77 2-Alkylhexahvdrobenzoselenazoles. by reaction of a-chlorocyclohexvl-amine, with selenocarboxamide,... 

Condensation of selenocarboxamides with a-chloro- or a-bromocarbonyl compounds gives access to a wide variety of substituted 1,3-selenazoles by choosing suitable reaction partners and, in most cases, they are produced in good to excellent yields [3, 14, 174], For example, the phenacetyl bromide (100) and selenobenza-mide (101) gave 2,4-diphenyl-l,3-selenazole (102) (Scheme 30) [174],... 

Hofmann (1889LA(250)294) was the first to report the synthesis of selenazoles in a modified Hantzsch reaction in which derivatives of selenocarboxamides are allowed to react with a-chlorocarboxyl compounds. Other substituted selenazoles are prepared similary (Scheme 19). 

A convenient method for the synthesis of selenocarboxamides (121) from aromatic and aliphatic nitriles using monoselenophosphate (122) has been elaborated. This method complements the previously reported methods since aqueous acidic conditions are used as opposed to basic conditions or BF3. OEt2 in... 

They resonate in the range of 3 = 900-1000 for example PhCID C(=Se)-OMe, 3 = 956,2 and I li ( ( Se) () Clf, /Bii. 3 = 933.- Selenocarboxamides, R-C(=Se)-NR R", show even lower Se chemical shifts. Since they are quite stable, a number of reports on these compounds have recently appeared. They show a typical chemical shift range of 3 = 700 100, depending on the organyl residues attached, but lower values nearly down to 3 = 300 may occur see for example compounds 137,2 ... 

The classical method of forming 1,3-selenazole derivatives involves a modification of the Hantzsch thiazole synthesis. For this purpose derivatives of selenocarboxamides, in place of thioamides, are allowed to react with ot-halocarbonyl compounds 16 to give the corresponding 1,3-selenazoles (17). - [Eq. (8)]. 

The above reaction was first reported by Hofmann. It permits the synthesis of a wide variety of compounds. By the use of suitable reaction partners, the selenocarboxamide as well as a-halocarbonyl components could be varied. The difficulty encountered in the synthesis of alkylselenocarbox-amides could be overcome by passing hydrogen selenide into a mixture of a nitrile and a-haloketone or 2-haloaldehyde acetal in the presence of condensation catalysts. [Eq. (9)]. Selenourea forms 2-aminoselenazoles. ... 

The modified Hantzsch synthesis first described by Hofmann <1889LA(250)294> has remained the general method for preparing 1,3-selenazoles. Depending on the substitution required in the selenazole the requisite selenocarboxamide and a-halocarbonyl derivatives are coupled (Scheme 7) <79HC(34)217>. Since a chlorooxirane is isomeric with an a-chlorocarbonyl, 2-aminoselenazoles are also formed with selenourea (Equation (6)) <81T2607>. The synthesis of a 5-quinonyl-l,3-selenazole... 

The discovery that elemental selenium could easily be reduced to hydrogen selenide with carbon monoxide in the presence of water and triethylamine led to the preparation of selenocarboxamidesThe in situ generation of hydrogen selenide was further employed under slightly modified conditions to give ] -substituted and disubstituted selenocarboxamides by reaction of the initially... 

Aromatic and heteroaromatic selenocarboxamides are obtained in high yield from nitriles and AljScj in a pyridine—NEtj-H20 system. ... 

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