Substitution Reactions on Carbon Atoms

Hie proposed participation of a Cu tlie diemistry of litliium diorganoaura graphic data for Cu species [104] bav Au and Cu [105]. 

Cuprates react rapidly witli allylic halides for acetates) [17, 23], propargyl halides for acetates) [ 106-108], and vinyloxiraties, often witli S 2 regioselectivity iSclieme 10.9) [17]. Hie reaction takes place witli emit stereodieniistry iwitli respect to tlie leaving group), while syn substitution occurs when an allylic carbamate is employed as tlie substrate [109]. 

Sn2 substitution reactions of alkyl halides with hard nucleophiles such as alkyl anions can be achieved most readily with the aid of organocopper chemistry [95]. Sn2 reactions with epoxides and aziridines are also synthetically useful [96]. The 

TO Mechanisms of Copper-mediated Addition and Substitution Reactions 

The proposed participation of a Cu intermediate is based on an analogy with the chemistry of Hthium diorganoaurate(I), R2Au Li [102, 103]. Recent crystallographic data for Cu species [104] have further supported the similarity between Au i and Cu i [105]. 

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Electrophilic substitution reactions on the carbon atoms of 1,3,4-thiadiazoles are rare due to the low electron density of ring carbons. G-Acylation can be accomplished via rearrangement of intermediate W-acylthiadiazolium salts while radical halogenation can give chlorinated or brominated 2-halo-5-substituted thiadiazoles. Examples can be found in CHEC(1984) <1984CHEC(6)545> and in Houben-Weyls Science of Synthesis <2004HOU(13)349>. 

Depending on the alcohol moieties present (i.e., quality of leaving group(s), presence of an aliphatic alcohol moiety), the neutral reaction as well as reactions with soft nucleophiles (e.g. HS-, CN, see Box 13.1) may also proceed by nucleophilic substitution at a carbon atom (C-0 cleavage). This is the case for trialkyl phosphates such as trimethyl and triethyl phosphate ... 

Simple nucleophilic substitutions at saturated carbon atoms are fundamental reactions found wherever organic chemistry is practised. They are used in industry on an enormous scale to make heavy chemicals and in pharmaceutical laboratories to make important drugs. They are worth studying for their importance and relevance,... 

Unlike any of the other acetylated glycosyl halides, the fluorides may be deacetylated without lo.ss or tsomerization of the halide function. This unique reaction can be effected either with alcoholic ammonia or with a catalytic amount of sodium methoxide in alcohol. In some instances, however, depending on the concentration of base and on the configuration and type of substitution at the carbon atom next to the glycosidic center, side-reactions occur that lead to glycoside or anhydride structures. ... 

Vinylsilanes have been widely recognized as facile intermediates for many sorts of applications39. While vinylsilanes undergo electrophilic substitution at the carbon atom containing the silyl group, the double-bond geometry is quite frequently retained. As a consequence vinylsilanes are well suited as precursors to a variety of reaction products with geometrically defined double bonds. Also feasible is an addition-elimination sequence, however here the reaction conditions have an influence on the stereochemistry of the reaction products. 

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