Imine alkylations

Imin Alkyl- bzw. Dialkylamin Carbonsaure (Aldehyd, Kcton) 358 f. 

Alkylation and hydrolysis of imines alkylation of aldehydes 10-107 Alkylation and hydrolysis of dithianes 10-108 Alkylation and hydrolysis of oxazines and similar compounds 10-109 Reaction of diazo aldehydes with boranes... 

A diastereoselective imine alkylation and a palladium-catalysed biaryl coupling were important steps in the diastereoselective synthesis of 6,7-dihydro-5//-dibenz[c,e]azepines (Scheme 7) starting from (R)-l-(2-methoxyphenyl)ethylamine. Selection for the... 

Zr-Catalyzed Enantioselective Imine Alkylations with Alkylzinc Reagents... 

As is also illustrated in Scheme 6.23, the optically enriched amino nitriles can be converted to the corresponding a-amino esters through a four-step sequence (74—> 75). Unlike the aforementioned imine alkylations with alkylzinc reagents, methylation of the phenolic OH is required, since the corresponding o-methoxy aniline is less reactive and affords significantly lower enantioselectivities similar observations are made when aniline is used. 

The studies summarized above clearly bear testimony to the significance of Zr-based chiral catalysts in the important field of catalytic asymmetric synthesis. Chiral zircono-cenes promote unique reactions such as enantioselective alkene alkylations, processes that are not effectively catalyzed by any other chiral catalyst class. More recently, since about 1996, an impressive body of work has appeared that involves non-metallocene Zr catalysts. These chiral complexes are readily prepared (often in situ), easily modified, and effect a wide range of enantioselective C—C bond-forming reactions in an efficient manner (e. g. imine alkylations, Mannich reactions, aldol additions). 

As the last point in Sect. IV, we discuss briefly the reactions of chiral sulfur compounds with electrophilic reagents. In contrast to nucleophilic substitution reactions, the number of known electrophilic reactions at sulfur is very small and practically limited to chiral tricoordinate sulfur compounds that on reacting with electrophilic reagents produce more stable tetracoordinate derivatives. It is generally assumed that the electrophilic attack is directed on the lone electron pair on sulfur and that the reaction is accompanied by retention of configuration. As typical examples of electrophilic reactions at tricoordinate sulfur, we mention oxidation, imination, alkylation, and halogenation. All these reactions were touched on in the section dealing with the synthesis of chiral tetracoordinate sulfur compounds. 

Finally, polymer 594 has been used as an arene-catalyst to activate nickel from nickel(II) chloride and lithium, in order to perform hydrogenation of different organic substrates such as afkenes, afkynes, carbonyl compounds and their imines, alkyl and aryl halides (chlorides, bromides and iodides), aromatic and heteroaromatic compounds as well as nitrogen-containing systems such as hydrazines, azoxy compounds or Af-amino oxides, giving comparable results to those obtained in the corresponding reaction in solution . 

Starting Imine Alkylation Conditions Config. of eea (%) Yield (%) Md (solvent)b Ref... 

Hydrolysis of enol esters 0-83 Reduction of acyl halides 0-84 Reduction of carboxylic acids, esters, or anhydrides 0-85 Reduction of amides 0-95 Alkylation and hydrolysis of imines, alkylation of aldehydes 0-97 Alkylation and hydrolysis of dithi-anes... 

In 2001, Hoveyda and co-workers disclosed Zr-catalyzed imine alkylations promoted by peptide-based chiral ligands 7 and 8 that afford arylimines 9 in 82-... 

Step b Two acid-catalyzed cyclizations ally silane addition to an iminium ion followed by intramolecular imine alkylation and loss of MeOH. 

The introduction of alkyl groups at the a-carbon of amino acids has been accomplished most efficiently by formation of imine esters. For example, the benzaldehyde imine of ethyl glycinate can be deproton-ated and alkylated (equation 39)." Other imines also have been used." Optical activity has been introduced by using chiral palla um ligands during the alkylation step, ° chiral alcohols to form the ester, and chiral ketones to form the imine." Alkylation of 2-pyrrole acetate esters has been accomplished in a similar fashion." ... 

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