RESUMO
An enantioselective copper-catalyzed asymmetric conjugate addition of Me2Zn to (Z)-nitroalkenes led to the formation of all-carbon quaternary stereogenic centers with high stereoselectivity. The key features of the new method are the unprecedented use of [(MeCN)4Cu]PF6 in conjunction with the Hoveyda ligand L1 and the use of (Z)-nitroalkene substrates so that undesired nitroalkene isomerization is minimized and enantioselectivity is enhanced dramatically. We also describe a novel, practical, and highly (Z)-selective nitroalkene synthesis.
Assuntos
Alcenos/química , Cobre/química , Nitrogênio/química , Compostos Organometálicos/química , Catálise , Cromatografia Líquida de Alta Pressão , Isomerismo , Ligantes , EstereoisomerismoRESUMO
Herein we describe the first use of disubstituted donors in the palladium-catalyzed trimethylenemethane (TMM) cycloaddition resulting in an enantioselective synthesis of highly substituted pyrrolidines. These cyanoalkyl donors 1 form all-carbon quaternary centers in a catalytic, asymmetric, and intermolecular manner uniquely using diamidophosphite ligands L2 and L3, generating synthetically important chiral building blocks in good yields and selectivities.
RESUMO
A general, efficient, and highly diastereoselective method for the synthesis of structurally and sterically diverse P-chiral phosphine oxides was developed. The method relies on sequential nucleophilic substitution on the versatile chiral phosphinyl transfer agent 1,3,2-benzoxazaphosphinine-2-oxide, which features enhanced and differentiated P-N and P-O bond reactivity toward nucleophiles. The reactivities of both bonds are fine-tuned to allow cleavage to occur even with sterically hindered nucleophiles under mild conditions.
Assuntos
Óxidos P-Cíclicos/síntese química , Fosfinas/síntese química , Óxidos P-Cíclicos/química , Ligantes , Estrutura Molecular , Fosfinas/química , EstereoisomerismoRESUMO
Carbamoyl anions, generated from N,N-disubstituted formamides and lithium diisopropylamide, add with high diastereoselectivity to chiral N-sulfinyl aldimines and ketimines to provide α-amino amides. The methodology enables the direct introduction of a carbonyl group without the requirement of unmasking steps as with other nucleophiles. The products may be converted to α-amino esters or 1,2-diamines. Iterative application of the reaction enabled the stereoselective synthesis of a dipeptide. Spectroscopic and computational studies support an anion structure with η(2) coordination of lithium by the carbonyl group.
Assuntos
Amidas/química , Amidas/síntese química , Iminas/química , Técnicas de Química Sintética , Dipeptídeos/síntese química , Dipeptídeos/química , Modelos Moleculares , Conformação Molecular , Estereoisomerismo , Especificidade por SubstratoAssuntos
Butanos/síntese química , Sulfonamidas/síntese química , Aminas/síntese química , Aminas/química , Aminoácidos/síntese química , Aminoácidos/química , Amino Álcoois/síntese química , Amino Álcoois/química , Aziridinas/síntese química , Aziridinas/química , Butanos/química , Catálise , Diaminas/síntese química , Diaminas/química , Iminas/síntese química , Iminas/química , Compostos Organometálicos/química , Oxirredução , Estereoisomerismo , Sulfonamidas/químicaRESUMO
A general, scalable, and highly diastereoselective aziridination of N-tert-butanesulfinyl ketimino esters is described. The methodology has been utilized to provide straightforward access to previously unobtainable, biologically relevant α-quaternary amino esters and derivatives starting from readily available precursors.