Amines thermal activation

Reaction selectivity of the parent ortho-QM has also been explored with a variety of amino acid and related species.30 In these examples, the rates of alkylation and adduct yields were quantified over a range of temperatures and pH values. The initial QM3 was generated by exposing a quaternary benzyl amine (QMP3) to heat or ultraviolet radiation (Scheme 9.10). Reversible generation of QM3 was implied by subsequent exchange of nucleophiles at the benzylic position under alternative photochemical or thermal activation.30 Report of this work also included the first suggestion that the reversible nature of QM alkylation could be used for controlled delivery of a potent electrophile. 

The upper temperature at which polyelectrolytes can be utilised can be extended by substitution of a polar organic solvent for water in the electrolyte. Conductivities of up to 1 Q 1m 1 have been obtained for sulphonated PEEK using anhydrous pyrazole and imidazole at 200 C (Kreuer et al., 1998). Solvents used to form electrolytes in Nafion membranes have included alcohols, amines, propylene carbonate, dimethoxyethane, dimethyl form-amide, dimethyl sulphoxide and TV-methyl pyrrolidone. Typical conductivities for the latter three solvents are 10 to 1 O-lm 1 at room temperature, and the conductivity is thermally activated with activation energies in the range 9 to 24 kJ/mol (Doyle et al., 2001). 

Under thermal activation conditions, ester 161 reacts with benzylamine to give a mixture of a-amino-p,y-unsaturated ester 164 and amide 165, but under 1.1 GPa pressure ester 161 gives the spiro-aziridines 162 and 163 in high yield and good diastereoselectivity. These are part of an attractive class of compounds that are formed by hetero-Michael addition of amine onto the unsaturated ester 161, followed by intramolecular nucleophilic substitution of the bromine atom (Scheme 7.41). ... 

Two new unsymmetric derivatives of l,2-bis-(5-phenyloxazol-2-yl)benzene (o-POPOP) under microwave exposure were synthesized by Lliashenko et al. (2011). In this reaction, fluorine was replaced by nucleophile such as hydroxyl ion or cyclic secondary amine. This reaction appears to be significantly more efficient as compared with conventional thermal activation. 

A surpnsing feature of the reactions of hexafluoroacetone, trifluoropyruvates, and their acyl imines is the C-hydroxyalkylation or C-amidoalkylaOon of activated aromatic hydrocarbons or heterocycles even in the presence of unprotected ammo or hydroxyl functions directly attached to the aromatic core Normally, aromatic amines first react reversibly to give N-alkylated products that rearrange thermally to yield C-alkylated products. With aromatic heterocycles, the reaction usually takes place at the site of the maximum n electron density [55] (equaUon 5). 

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