Alkylation

About: Alkylation is a research topic. Over the lifetime, 29915 publications have been published within this topic receiving 464944 citations. The topic is also known as: alkylation reaction.

Palladium-Catalyzed Cross Coupling of Secondary and Tertiary Alkyl Bromides with a Nitrogen Nucleophile

Abstract: We report a new class of catalytic reaction: the thermal substitution of a secondary and or tertiary alkyl halide with a nitrogen nucleophile. The alkylation of a nitrogen nucleophile with an alkyl halide is a classical method for the construction of C–N bonds, but traditional substitution reactions are challenging to achieve with a secondary and or tertiary alkyl electrophile due to competing elimination reactions. A catalytic process could address this limitation, but thermal, catalytic coupling of alkyl halides with a nitrogen nucleophile and any type of catalytic coupling of an unactivated tertiary alkyl halide with a nitrogen nucleophile are unknown. We report the coupling of unactivated secondary and tertiary alkyl bromides with benzophenone imines to produce protected primary amines in the presence of palladium ligated by the hindered trialkylphosphine Cy2t-BuP. Mechanistic studies indicate that this amination of alkyl halides occurs by a reversible reaction to form a free alkyl radical.

Kinetic NMR and density functional study of benzene H/D exchange in zeolites, the most simple aromatic substitution

Abstract: Nuclear magnetic resonance (NMR) studies of reactions on solid acids and bases, including zeolites, metal oxides, and metal halides, have characterized persistent intermediates, and the range of these investigations has been extended by monitoring label scrambling. However, there have been no detailed in situ NMR kinetic measurements. We have carried out the first such study, a detailed investigation of the H/D exchange reaction of benzene, which is the most simple example of the class of aromatic substitution reactions that includes important processes such as toluene alkylation. The avoidance of a free cation even for the energetically less demanding reaction studied here suggests that free cations in acid catalysis by zeolites at low temperature may be the exception rather than the rule; indeed, the only such species observed spectroscopically have been exceptionally stable cations. 27 refs., 3 figs.

General method for the asymmetric synthesis of α-amino acids via alkylation of the chiral nickel(II) Schiff base complexes of glycine and alanine

Abstract: Nickel(II) complexes of Schiff bases derived from (S)-o-[(N-benzylprolyl)amino] benzaldehyde and alanine (3), or (S)-O-[(N-benzylpropyl)amino]benzophenone and alanine (4), or glycine (5) have been used for the asymmetric synthesis of α-amino acids under a variety of conditions. The method of choice consists of the reaction of the corresponding complex with the appropriate alkyl halide in DMF at 25 °C using solid NaOH as a catalyst. Low diastereoselective excess (d.e.) is observed for the alkylation of complex (3) with benzyl bromide and allyl bromide. Large selectivity (80%) is observed for the alkylation of complex (4). Optically pure (R)- and (S)-α-methyl-α-amino acids [(S)-α-methylphenylalanine, (S)-α-allylalanine and (S)-O-benzyl-α-methyltyrosine] were obtained (70–90%) after the alkylated diastereoisomeric complexes had been separated on SiO2 and hydrolysed with aqueous HCl. The initial chiral reagents were recovered (80–92%). The alkylation of complex (5) gave (S)-alanine, (S)-valine, (S)-phenylalanine, (S)-tryptophan, (S)-isoleucine, (S)-2-aminohexanoic acid, and 3,4dimethoxyphenylalanine with optical yields of 70–92%. The optically pure α-amino acids were obtained after the separation of the alkylated diastereoisomeric complexes on SiO2. The stereochemical mechanism of the alkylation reaction is discussed.