Chiral complexes formed by phosphoramidites such as (S a ,R,R)-9 and Cu(OTf) 2 are excellent catalysts for the general 1,3-dipolar cycloaddition between azomethine ylides and nitroalkenes affording the corresponding tetrasubstituted proline esters mainly as exo-cycloadducts in high er at room temperature. The exo-cycloadducts can be obtained in enantiomerically pure form just after simple recrystallization. DFT calculations support the stereochemical results.Substituted prolinates 1, obtained from the corresponding 1,3-dipolar cycloadditions (1,3-DC) 1 between glycine ester aldimines and nitroalkenes, are important inhibitors of α 4 β 1 -integrin-mediated hepatic melanoma metastasis. 2 The most simple prolines exo-2 have been recently used as chiral organocatalysts in aldol reactions. 3 In particular, for the asymmetric 1,3-DC of nitroalkenes as dipolarophiles chiral copper(I) complexes, formed from ferrocenyl-type phosphanes, have been mainly used as catalysts. 3,4 Copper(I) complexes 3, 4a,c 4, 4b,e and 5, 3 generally afforded exo 5 -cycloadducts, whereas the corresponding endodiastereomers have been prepared using complex 6. 3 However, when copper(II) triflate and chiral ligand PyBidine 6 were combined the resulting catalyst 7 afforded
Palladium-catalyzed cross-coupling of aryllithium reagents with 2-alkoxy-substituted aryl chlorides is described. The reactions proceed under mild conditions with short reaction times and provide a wide range of 2-alkoxy-substituted biaryls. This new methodology is applied to the efficient preparation of 3,3'-diaryl BINOLs and represents the first synthesis of this important class of chiral compounds from the corresponding 3,3'-dichloro BINOLs.
Abstract. Chiral complexes formed by privileged phosphoramidites and silver triflate or silver benzoate are excellent catalysts for the general 1,3-dipolar cycloaddition between azomethine ylides generated from α-amino acids derived imino esters and nitroalkenes affording with high dr the exo-cycloadducts 4,5-trans-2,5-cis-4-nitroprolinates in high ee at room temperature. In general, better results are obtained using silver than copper(II) complexes. In many cases the exo-cycloadducts can be obtained in enantiomerically pure form just after simple recrystallization.The mechanism and the justification of the experimentally observed stereodiscrimination of the process are supported by DFT calculations. These enantiomerically enriched exonitroprolinates can be used as reagents for the synthesis of nitropiperidines, by ester reduction and ring expansion, which are inhibitors of farnesyltransferase.
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