RESUMO
Using newly designed α-imino amide surrogates and azlactones as amphiphilic reactants, catalyzed by a chiral bifunctional guanidine, the construction of chiral 3,4-diaminopyrrolidine-2,5-diones and their derivatives was realized via formal [3+2]-cyclization. The role of guanidine as a multiple hydrogen bond donor was demonstrated by DFT calculations.
Assuntos
Amidas , Ciclização , Amidas/química , Catálise , Estereoisomerismo , Guanidina/químicaRESUMO
A chiral Lewis acid-catalyzed enantioselective formal [2 + 2 + 2] cycloaddition of 1,3,5-triazinanes with azlactones or ß,γ-unsaturated pyrazole amides was developed to synthesize chiral tertiary/quaternary tetrahydropyrimidin-4-one derivatives with good yields and enantioselectivities. Two competitive reaction pathways were proposed based on experiments.
RESUMO
A highly enantioselective formal conjugate allyl addition of allylboronic acids to ß,γ-unsaturated α-ketoesters has been realized by employing a chiral NiII /N,N'-dioxide complex as the catalyst. This transformation proceeds by an allylboration/oxy-Cope rearrangement sequence, providing a facile and rapid route to γ-allyl-α-ketoesters with moderate to good yields (65-92 %) and excellent ee values (90-99 % ee). The isolation of 1,2-allylboration products provided insight into the mechanism of the subsequent oxy-Cope rearrangement reaction: substrate-induced chiral transfer and a chiral Lewis acid accelerated process. Based on the experimental investigations and DFT calculations, a rare boatlike transition-state model is proposed as the origin of high chirality transfer during the oxy-Cope rearrangement.
RESUMO
Efficient enantioselective insertion of α-diazoesters into the N-H bond of N-sp2-hybridized benzophenone imine was realized by using Rh2(esp)2 and chiral guanidine cooperative catalysis. Both aliphatic and aromatic substituted α-amino esters were obtained in high yields (up to 99%) and good enantioselectivities (up to 95.5 : 4.5 er) under mild reaction conditions.
