Carbanions ethenyl

The interesting zwitterionic compound (39) with the cationic component a butadien-2-yl cation was obtained by reaction of l,4-di(t-butyl)butadiyne with 2 mol of di(r-butyl)aluminium hydride, with the structure being established by X-ray analysis.80 The reactions of the l,2-diferrocenyl-3-(methylthio)cyclopropenylium ion with carbanions derived from active methylene compounds were investigated.81 Products were derived by ring opening of the cyclopropene ring after the initial carbanion addition. The bis(ferrocenylethynyl)phenylmethylium cation (Fc-C=C-)2C+Ph (Fc = ferrocenyl) was prepared 82 This cation proved to be much less stable than its bis-ethenyl analogue (Fc-CH=CH-)2C+Ph. 

A convenient synthesis of diethyl (2-arylethenyl)phosphonates starts with readily available diethyl methylphosphonate this is converted into its carbanion (BuLi) and the latter acted upon by an appropriate aldehyde or ketone. The resultant (2-substituted-2-hydroxyethyl)phosphonate is phosphory-lated and, without isolation of the phosphate ester, a treatment with KOBu eliminates diethyl phosphate and yields the desired product Other diethyl (2,2-disubstituted-ethenyl)phosphonates have been prepared by the addition of organomagnesium-copper reagents to diethyl ethynylphos-phonate ... 

Introduction of arylsulfonylmethyl substituents into nitroheteroaromatic rings is of great practical value because these sulfones are versatile intermediates in organic synthesis. Nitrobenzyl aryl sulfones and their heterocyclic analogues can easily be transformed into the corresponding ethenyl derivatives by a simple alkylation with simultaneous elimination of arylsulfinate anion [125]. Diethyl methylenemalonate substituent can be introduced in the positimi 4- of 5-nitroimidazole via the VNS reaction of 5-nitroimidazole with the carbanion of chloromethyl phenyl sulfone [112, 124], followed by condensation of the obtained 4-(phenylsulfonyl)methyl derivative with diethyl bromomalonate or diethyl ketomalonate (Scheme 33) [126]. 

Xu Y, Jin F, Huang W. (Trifluoroisopropenyl)tributyltin as a novel a-(trifluoromethyl)ethenyl carbanion synthetic equivalent. Preparation and its palladium-promoted coupling with acyl chlorides. J. Org. Chem. 1994 59 2638-2641. 

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