ABSTRACT
[reaction: see text] Olefinic pyrazines are found to react with benzene in CF3SO3H and give anti-Markovnikov-type addition products. We propose that this is caused by two effects: destabilization of the carbocationic intermediates that would lead to Markovnikov-type products and the generation of a considerable amount of positive charge at the terminal carbon of the olefinic groups. This suggests that acid-catalyzed addition reactions can give anti-Markovnikov-type products when a multiply charged (i.e., superelectrophilic) group is adjacent to the olefinic site.
Subject(s)
Pyrazines/chemistry , Alkenes/chemistry , Benzene/chemistry , Catalysis , Electrochemistry , Indicators and Reagents , Molecular StructureABSTRACT
A variety of aminoalkynes and related heterocycles are reacted in the Bronsted superacid CF(3)SO(3)H (triflic acid), and products are obtained in generally good yields (69-99%) from Friedel-Crafts-type reactions. The reactions are consistent with the formation of novel dicationic intermediates having a vinyl cationic site and an adjacent protonated N-heterocycle or ammonium cation.
Subject(s)
Alkynes/chemistry , Amines/chemistry , Heterocyclic Compounds/chemistry , Catalysis , Cations/chemistry , Indicators and Reagents , Molecular Structure , Quaternary Ammonium Compounds/chemistryABSTRACT
In the Brønsted superacid CF(3)SO(3)H (triflic acid), amides are able to form reactive, dicationic electrophiles. It is shown that these dicationic intermediates participate in two distinctly different types of electrophilic reactions. The protonated amide increases the reactivity of an adjacent electrophilic group, and the protonated amide group itself shows enhanced reactivity arising from an adjacent cationic charge. In the latter case, several types of amides are even capable of reacting with benzene by Friedel-Crafts acylation. [reaction--see text]
Subject(s)
Amides/chemistry , Protons , Acylation , Cations/chemistry , Magnetic Resonance Spectroscopy , Models, Chemical , Molecular Structure , TemperatureABSTRACT
The chemistry of cinnamic acids and related compounds has been studied. In superacid-catalyzed reactions with arenes, two competing reaction mechanisms are proposed. Both mechanisms involve the formation of dicationic intermediates (superelectrophiles), and the reactions can lead to either chalcone-type products or indanone products. The direct observation of a dicationic species (by low-temperature (13)C NMR) is reported. We provide clear evidence that protonated carboxylic acid groups (or the corresponding acyl cation) can enhance the reactivity of an adjacent electrophilic center. Triflic acid is also found to be an effective acid catalyst for the direct synthesis of some electron-deficient chalcones and heterocyclic chalcones from cinnnamic acids.
Subject(s)
Chalcone/chemistry , Cinnamates/chemistry , Acylation , Carboxylic Acids/chemistry , Catalysis , Chalcone/analogs & derivatives , Electrochemistry , Indicators and Reagents , Magnetic Resonance Spectroscopy , Mesylates/chemistry , Molecular StructureABSTRACT
This paper describes the superacid-catalyzed chemistry of olefinic amines and related compounds. A variety of olefinic amines are found to react with benzene in CF(3)SO(3)H (triflic acid) to give addition products in good yields (75-99%), including the pharmaceutical agents fenpiprane and prozapine. A general mechanism is proposed that invokes the formation of reactive, dicationic electrophiles and the direct observation of a diprotonated species is reported from low-temperature NMR experiments. This chemistry is also used to conveniently prepare functionalized polystyrene beads having pendant amine groups.
