Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

1.2.5- Thiadiazoles, amino-, halogenation

The enhanced reactivity of 5-halogeno-l,2,4-thiadiazoles over 3-halogeno-l,2,4-thiadiazoles has been mentioned before (see Section 5.08.7.1). Nucleophilic substitution at this center is a common route to other 1,2,4-thiadiazoles, including 5-hydroxy, alkoxy, mercapto, alkylthio, amino, sulfonamido, hydrazino, hydroxylamino, and azido derivatives. Halogens in the 3-position of 1,2,4-thiadiazoles are inert toward most nucleophilic reagents, but displacement of the 3-halogen atom can be achieved by reaction with sodium alkoxide in the appropriate alcohol <1996CHEC-II(4)307>. [Pg.499]

The transformation of 1,2,4-thiadiazoles bearing a reactive substituent such as amino or halogen group in the 5-position is the most useful method for the synthesis of 5-substituted 1,2,4-thiadiazole derivatives. The latter compounds can be reacted with nucleophiles to afford a wide range of derivatives this is not the case for 3-halogen-substituted compounds. [Pg.508]

As mentioned in Section 4.10.6.5, substituents on C(2) and C(5) are strongly activated and control the reactivity of the thiadiazole molecule as a whole. The amino group is by far the most popular substituent for further modifications, due to its nucleophilicity and ease of ring formation with the annular N(3). To a somewhat lesser extent, the thiol group has also been utilized in further derivatizing, with the carbon and halogen substituents being the least amenable to further reactions. [Pg.393]

Sulfur-linked substituents are usually prone to oxidation by halogens. In aqueous solution, chlorine converted 5-amino-3-benzylthio-1,2,4-thiadiazole successively into sulfoxide and sulfone, but in glacial acetic... [Pg.372]

The scope of the synthesis is greatly widened by the preliminary preparation of the N-halogenoamidines (56), preferably in situ subsequent displacement of halogen by thiocyanate results in the formation of the desired 5-amino-1,2,4-thiadiazoles (58) in good yields (50-80%).6,79, 80 The use of formamidine affords the parent, 5-amino-1,2,4-thiadiazole (58 R = H) while use of AT-methylformamidine (59) leads to 5-imino-4-methyl-Zl4-1,2,4-thiadiazolines (60).81... [Pg.135]

Amino-l,2,4-thiadiazoles are usually prepared by treating amidine hydrochlorides with halogen and thiocyanates to yield the 3-alkyl derivatives or treating alkylisothiouronium salts similarly to yield the 3-alkylthio derivatives (56CB2742). Diazonium salts derived from 5-amino-l,2,4-thiadiazole derivatives, which are prepared in acetic acid, are extremely reactive and are capable of coupling with m -xylene (60CB397). [Pg.330]

Due to the low electron density at the carbon atoms in 1,3,4-thiadiazole, such reactions as nitration, sulfonation, acetylation, halogenation, etc. normally do not take place. However, 2-amino-substituted 1,3,4-thiadiazoles (73a-i) react with bromine in acetic acid to give the 5-bromo derivatives (74a-i). Similarly, the thiadiazolines (75b) and (75d-f) yield the corresponding 5-bromo derivatives (76b) and (76d-f). The thiadiazoline (75a), however,... [Pg.560]

In a variation of this synthesis, the amidine is N-halogenated prior to its condensation with an isothiocyanate ester the resulting IV-haloimidoyl-thioureas (238) are readily cyclized to 239 by alkalis. By employing bromine in conjunction with methylene chloride-aqueous alkali as the reaction medium, the reaction may be performed in one operation. 3-Trichloromethyl-5-(substituted)amino-l,2,4-thiadiazoles have been produced by this method.187 The use of potassium ethyl xanthate similarly yields the 5-ethoxy analogs (240 e.g., R = CC13, R1 = Et) directly, with elimination of the elements of hydrogen sulfide.188... [Pg.333]


See other pages where 1.2.5- Thiadiazoles, amino-, halogenation is mentioned: [Pg.485]    [Pg.485]    [Pg.105]    [Pg.158]    [Pg.860]    [Pg.200]    [Pg.497]    [Pg.321]    [Pg.329]    [Pg.373]    [Pg.136]    [Pg.142]    [Pg.148]    [Pg.187]    [Pg.461]    [Pg.860]    [Pg.158]    [Pg.478]    [Pg.505]    [Pg.558]    [Pg.585]    [Pg.200]    [Pg.131]    [Pg.174]    [Pg.105]    [Pg.773]    [Pg.105]    [Pg.773]    [Pg.860]    [Pg.158]    [Pg.478]    [Pg.505]    [Pg.558]    [Pg.860]   
See also in sourсe #XX -- [ Pg.47 , Pg.170 ]




SEARCH



1,2,3-thiadiazole

1,2,5-Thiadiazoles

1,3,4-Thiadiazol

1.2.5- Thiadiazole halogenation

2-Amino-1,3,4-thiadiazole

Thiadiazoles, amino

© 2024 chempedia.info