Tertiary amines electron withdrawing groups

An alkene activated by an electron-withdrawing group—often an acrylic ester 2 is used—can react with an aldehyde or ketone 1 in the presence of catalytic amounts of a tertiary amine, to yield an a-hydroxyalkylated product. This reaction, known as the Baylis-Hillman reaction, leads to the formation of useful multifunctional products, e.g. o -methylene-/3-hydroxy carbonyl compounds 3 with a chiral carbon center and various options for consecutive reactions. 

The reaction starts with the nucleophilic addition of a tertiary amine 4 to the alkene 2 bearing an electron-withdrawing group. The zwitterionic intermediate 5 thus formed, has an activated carbon center a to the carbonyl group, as represented by the resonance structure 5a. The activated a-carbon acts as a nucleophilic center in a reaction with the electrophilic carbonyl carbon of the aldehyde or ketone 1 ... 

A quaternary ammonium species 1, bearing an electron-withdrawing group Z a to the nitrogen center, can rearrange to a tertiary amine 3, when treated with a strong base. This reaction is known as the Stevens rearrangement. ... 

A chiral auxiliary-based approach has been developed for the preparation of chiral, non-racemic cyclopropyhnethylamines that are not protected with electron-withdrawing groups. The cyclopropanation of ally he tertiary amines bearing a -hydroxide occurred... 

Selenium-containing six-membered ring heterocycles have proved to be useful catalysts in a variety of transformations. The Baylis-Hillman reaction involves the reaction of alkenes containing electron-withdrawing groups such as a,/3-unsaturated carbonyl compounds with aldehydes leading to carbon-carbon bond formation (Equation 79). The reaction is promoted by tertiary amines such as l,4-diazabicyclo[2.2.2]octane (DABCO), or tertiary phosphines and Lewis acids. Unfortunately, the Baylis-Hillman reaction is severely limited because it proceeds only very slowly <1998CC197>. Much research has been carried out in attempts to increase the rate of this reaction. 

Due to the electrophilic nature of osmium tetroxide, electron-withdrawing groups connected to the alkene double bond retard the dihydroxylation. This is in contrast to the oxidation of alkenes by Potassium Permanganate, which preferentially attacks electron-deficient double bonds. However, in the presence of a tertiary amine such as pyridine, even the most electron-deficient alkenes can be osmylated by osmium tetroxide (eq 4). The more highly substituted double bonds are preferentially oxidized (eq 5). 

Reaction of peracids with quinolines and isoquinolines affords the corresponding A-oxides. Typical conditions are treatment of heterocycles with RCO2H in the presence of H2O2 at -100 C or /w-CPBA at 0 C. The quinoline/isoquinoline nitrogen atom reacts less readily with peracids than the tertiary amines. Large substituents and electron-withdrawing groups slow the reaction. 

A quatemaiy ammonium salt containing an electron-withdrawing group Z on one of the caibons attached to the nitrogen is treated with a strong base to give a rearranged tertiary amine. 

Sulphonyl Halides and Sulphenes.—It is becoming clear that reactions of alkanesulphonyl chlorides in the presence of a tertiary amine are likely to give poor yields of simple sulphonation products, due to the formation of sulphenes (RCHaSOgCl RCH=SOa) and artefacts resulting from them. Electron-withdrawing groups in the substituent facilitate sulphene... 

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