Biomedical subjects
Publications and source records attributed to Stephen L Buchwald.
A Ni(0)-BINAP system is utilized for the highly enantioselective alpha-arylation of alpha-substituted gamma-butyrolactones with aryl chlorides and bromides. alpha-Quaternization is achieved in moderate to excellent yields. Furthermore, the rate accelerating effect caused by the addition of Zn(II) salts is investigated.
Herein, we report the kinetic and the dynamic kinetic resolutions of racemic 3,5-dialkyl-2-cyclopenten-1-ones. Kinetic resolution, with good selectivity factors (25-52), was achieved by conjugate reduction with catalytic CuCl/NaOt-Bu/(S)-p-tol-BINAP and stoichiometric quantities of poly(methylhydrosiloxane) (PMHS). When stoichiometric amounts of NaOt-Bu and t-BuOH were included in the reaction mixture, rapid racemization of the starting material occurred allowing for the dynamic kinetic resolution of the cyclopentenone substrates. In this process, chiral 2,4-dialkylcyclopentanones were isolated with high stereoselectivity (ee > or = 91%, dr > or = 90:10) and in high yield (> or =89%).
[reaction: see text] A simple and mild method for the coupling of aryl iodides and aliphatic alcohols that does not require the use of alkoxide bases is described. The reactions can be performed in neat alcohol. For more precious alcohols, the etherification was carried out in toluene as solvent using 2 equiv of alcohol. Additionally, the cross-coupling of an optically active benzylic alcohol with an unactivated aryl halide was demonstrated to proceed with complete retention of configuration.
[reaction: see text] New phosphine ligands possessing both axial chirality and a chirogenic phosphorus center were prepared from (R)-2-bromo-2'-N,N-(dimethylamino)-1,1'-binaphthyl (1) via a simple Li-halogen exchange protocol. The asymmetric vinylation of a ketone enolate with (R,R(P))-2-(tert-butylphenylphosphino)-2'-N,N-(dimethylamino)-1,1'-binaphthyl (2a) afforded the coupling product with good enantiomeric excess.
[reaction: see text] A mild method for the copper-catalyzed amination of aryl iodides is reported. This operationally simple C-N bond-forming protocol uses CuI as the catalyst and ethylene glycol as ligand in 2-propanol. A variety of functionalized aryl iodides as well as several amines were efficiently coupled using this method. This catalytic amination procedure is relatively insensitive to moisture and can be performed under an air atmosphere with comparable yield. Preliminary results on the amination of aryl bromides are also described.
A new catalyst system for the enantioselective alpha-arylation of ketones is reported. This catalyst, prepared from Pd(2)(dba)(3) and a bulky dialkylphosphino-binaphthyl ligand, is able to effect the asymmetric arylation of ketone enolates with aryl bromides utilizing NaO(t)()Bu as base. These new catalysts enjoy much higher reactivity than previous systems; arylation reactions could be effected at room temperature with only 2 mol % of the Pd catalyst. The coupling of alpha-alkyl-alpha'-protected cyclopentanones proceeded in high yield, and the resulting quaternary stereogenic center was installed in up to 94% ee.
A catalyst system for the preparation of biaryls containing four ortho substituents via Suzuki coupling is described. The combination of a catalytic quantity of Pd2(dba)3 with either an electron-rich biarylphosphine or DPEPhos is effective using a wide range of substrates. The X-ray crystal structure of (dba)Pd(2-(9-phenanthryl)phenyl-dicyclohexylphosphine), in which the Pd is coordinated to the 9,10-double bond of the phenanthryl group, is also reported.
The Pd-catalyzed intramolecular alpha-arylation of alpha-amino acid esters is described. Starting from readily available amino acids, the synthesis of a variety of isoindolines and tetrahydroisoquinoline carboxylic acid esters has been accomplished. Additionally, fused tricyclic systems can be efficiently prepared from cyclic amino acid esters. Reaction conditions have been found that allow the use of tert-butyl ester and N-(benzyloxycarbonyl) protecting groups.
[reaction: see text] A general method for the synthesis of alpha-aryl malonates is described. The coupling of an aryl iodide and diethyl malonate in the presence of Cs(2)CO(3) and catalytic amounts of copper(I) iodide and 2-phenylphenol affords the alpha-aryl malonate in good to excellent yields. The mild reaction conditions and high levels of functional group compatibility make this an attractive synthetic alternative to previous methods.
A general protocol for the Pd-catalyzed-arylation of nitroalkanes is described. Substituted aryl bromides as well as aryl chlorides can be coupled efficiently with a variety of nitroalkanes under mild conditions to selectively yield the monoarylated products. This method tolerates a number of functional groups including ketones, esters, and olefins. Notably, the arylation of nitroalkanes can be effected chemoselectively over ketone and ester arylation.