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Linear Product (linear + product)
Selected AbstractsBetter Performance of Monodentate P -Stereogenic Phosphanes Compared to Bidentate Analogues in Pd-Catalyzed Asymmetric Allylic AlkylationsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2010Arnald Grabulosa Abstract The cationic allylpalladium complexes 3a,3f, 4a, 4e, 5e of type [Pd(,3 -2-Me-C3H4)P2]PF6 were synthesized using a group of monodentate P -stereogenic phosphanes, P=PPhRR, (a,f) and diphosphanes (PhRPCH2)2 (1a, 1e) or PhRPCH2Si(Me)2CH2PPhR (2e). The analogous cationic complexes with the disubstituted allyl group (,3 -1,3-Ph2 -C3H3) and monodentate phosphanes were not isolated as stable solids; only [PdCl(,3 -1,3-Ph2 -C3H3)P] (6a, 6d) were obtained. Palladium allyl complexes were screened as precatalysts in the allylic substitution of rac -3-acetoxy-1,3-diphenyl-1-propene (I) and (E)-3-acetoxy-1-phenyl-1-propene (III) with dimethyl malonate as the nucleophile. The various catalytic precursors showed a wide range of activity and selectivity. The bismonodentate phosphane complexes 3 are more active than the bidentate analogues. With regard to the regioselectivity, precursors containing monodentate phosphanes favour the formation of the linear product in the allylic substitution of cinnamyl acetate (III) compared with those containing bidentate phosphanes. With substrate I, compounds with the diphosphanes 1a and 1e, containing a five-membered chelate ring, gave low enantioselectivities (less than 10,% ee), but those with the diphosphane 2e, forming a six-membered chelate ring or with two monodentate phosphanes, afforded products with moderate enantioselectivity under standard conditions (ee up to 74,%). The results show that the performance of precursors containing monodentate phosphanes was superior to those containing bidentate ligands in both activity and selectivity. [source] Lewis Acid Controlled Regioselectivity in Styrene HydrocyanationCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2009Laura Bini Abstract According to present knowledge, the Ni-catalyzed hydrocyanation of styrene leads predominantly to the branched product 2-phenylpropionitrile (98,%). We observed a dramatic inversion of the regioselectivity upon addition of a Lewis acid. Up to 83,% of the linear product 3-phenylpropionitrile was obtained by applying phosphite ligands in the presence of AlCl3. The mechanism of the Ni-catalyzed reaction and the influence of additional Lewis acids have been investigated by means of deuterium labeling experiments, NMR studies, and DFT calculations. Furthermore, the behavior of different Lewis acids, such as CuCN, could be rationalized and predicted by DFT calculations. [source] Highly Selective Hydroaminomethylation of Internal Alkenes To Give Linear AminesCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2006Moballigh Ahmed Dr. Abstract The application of phenoxaphosphino-modified Xantphos-type ligands (1,9) in the rhodium-catalyzed hydroaminomethylation of internal olefins to give linear amines is reported. Excellent chemo- and regioselectivities have been obtained through the use of 0.1 mol,% [Rh(cod)2]BF4/0.4 mol,% xantphenoxaphos (1), providing a practical and environmentally attractive synthetic route for the preparation of amines from internal alkenes. For the first time, both functionalized internal olefins and mixtures of internal and terminal olefins have been converted highly selectively into linear amines. Investigations of the effects of the calculated natural bite angles of ligands on hydroaminomethylation shows that the regioselectivity for the linear product follows a similar trend to that seen in the hydroformylation of internal alkenes with the aid of these ligands. Hydroaminomethylation and each of its individual steps were monitored by high-pressure infrared spectroscopy. The results suggest that hydroaminomethylations take place by a sequential isomerization/hydroformylation/amination/hydrogenation pathway. [source] Bulky Monodentate Phosphoramidites in Palladium-Catalyzed Allylic Alkylation Reactions: Aspects of Regioselectivity and EnantioselectivityCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2004Maarten D. K. Boele Dr. Abstract A series of bulky monodentate phosphoramidite ligands, based on biphenol, BINOL and TADDOL backbones, have been employed in the Pd-catalysed allylic alkylation reaction. Reaction of disodium diethyl 2-methyl malonate with monosubstituted allylic substrates in the presence of palladium complexes of the phosphoramidite ligands proceeds smoothly at room temperature. The regioselectivities observed depend strongly on the leaving group and the geometry of the allylic starting compounds. Mono-coordination occurs when these ligands are ligated in [Pd(allyl)(X)] complexes (allyl=C3H5, 1-CH3C3H4, 1-C6H5C3H4, 1,3-(C6H5)2C3H3; X=Cl, OAc). The solid-state structure determined by X-ray diffraction of [Pd(C3H5)(1)(Cl)] reveals a non-symmetric coordination of the allyl moiety, caused by the stronger trans influence of the phosphoramidite ligand relative to X,. In all of these complexes, the syn,trans isomer is the major species present in solution. Because of fast isomerisation and high reactivity of the syn,cis complex, the major product formed upon alkylation is the linear product, especially for monosubstituted phenylallyl substrates in the presence of halide counterions. In the case of biphenol- and BINOL-based phosphoramidites, however, a strong memory effect is observed when 1-phenyl-2-propenyl acetate is employed as the substrate. In this case, nucleophilic attack competes effectively with the isomerisation of the transient cinnamylpalladium complexes. The asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate afforded the chiral product in up to 93,% ee. Substrates with smaller substituents gave lower enantioselectivities. The observed stereoselectivity is explained in terms of a preferential rotation mechanism, in which the product is formed by attack on one of the isomers of the intermediate [Pd{1,3-(C6H5)2C3H3}(L)(OAc)] complex. [source] | ||||||||||