N electron-withdrawing

Carbenes with a n-Electron-Donating and a n-Electron-Withdrawing Heteroatom Substituent (D-C-W)... 

Alkene complexes of platinum(O) react with strong acids to undergo protonation at th< alkene and yield the alkyl complex (equation 263).803 Since platinum alkyl complexes having n< electron-withdrawing groups on carbon are frequently unstable to electrophiles, the products o HX on platinum(O) alkene complexes are often dihaloplatinum(II) complexes (equatioi 264). 

However, it has been shown that substituents can change the position of the cycloheptatriene/ norcaradiene equilibrium. Thus n-electron-withdrawing substituents in 1 (X = Y = CN X = COjH, Y = H ) are able to stabilize the norcaradiene structure by shortening the distal (C2-C3) bond and lengthening the vicinal (C1-C2, C1-C3) bonds. With 7r-electron-do-nating substituents the situation is more complex. Only strong n-donors (e.g. 0 , CHj) effect stabilization by lengthening the cyclopropane bonds."... 

A similar acceleration owing to the influence of N-electron-withdrawing group was observed by other authors (87USP4663334) for/V-acetyl-4-iodopyrazole in the reaction with alkynes [Pd(PPh3)2Cl2, Cul, triethylamine, THF, room temperature, 1 h, 20°C]. 

Silver-catalyzed cyclization—stannylation of o-alkynylanihnes carrying N-electron-withdrawing groups with 2-tributylstannylfuran provided a straightforward route to (3-indolyl)stannanes (13CC11794). 

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