Electron-withdrawing groups remote

Selective chlorination of the 3-position of thietane 1,1-dioxide may be a consequence of hydrogen atom abstraction by a chlorine atom. Such reactions of chlorine atoms are believed to be influenced by polar effects, preferential hydrogen abstraction occurring remotely from an electron withdrawing group. The free radical chain reaction may be propagated by attack of the 3-thietanyl 1,1-dioxide radical on molecular chlorine. 

Fig. 9 Enzymatic mechanism involved in the formation of estrogens. A The sulfatase pathway. B,C Structure of the potent STS inhibitors EMATE and COUMATE. D New pharmacophore for the inhibition of estrone sulfatase R general carbon backbone (aromatic or aliphatic), X electron withdrawing groups (e.g. nitro), Y additional functionality including fused or adjacent/remote ring structures so as to meet the log requirement...

Elemental fluorine can be used to replace relatively electron rich C-H bonds by C-F. In particular, tertiary hydrogen atoms which are remote from electron withdrawing substituents can be selectively replaced by fluorine and, where there is more than one tertiary hydrogen atom in the substrate, that with the higher electron density is replaced (Fig. 44). In contrast, where there is an electron withdrawing group close to tertiary hydrogen, very little reaction with fluorine takes place and, consequently, when one fluorine atom has been introduced into a molecule further reaction is often inhibited. 

By use of Pybox substituted at the 4-position of the pyridine skeleton, the remote electronic substituent effect for asymmetric induction was found to show that enantiomeric excesses became higher with electron-withdrawing groups and lower with electron-donating groups, but the ratios of the trans-to-cis products were not influenced by the substituents [27]. 

Besides activating the triple bond towards Michael addition the electron-withdrawing group (EWG) introduced by Sonogashira coupling can also exert an activation of the remote propargyl position (Scheme 8). This propargyl activation could for... 

Conversely, if the electron-withdrawing groups are present in C-4 and/or C-6 (as in 32 or 43), the lone pair on 0-3 will be of lower availability, which significantly increases the energy barrier for the formation of the partially acylated oxocarbenium ion. Alternatively, in the case of per-acylated derivatives 44 or 30, the influence of the remote substituents is diminished by the fact that the formed glycosyl cation can be stabilized by the acyloxonium ion formation (69). 

Directing Effect of Remote Electron-Withdrawing Groups in Glycopyranosylations... 

REWG remote electron-withdrawing group Lg leaving group... 

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