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At least 181 records · Page 10Linked to original sources
PubMed2001

Condensation of laterally lithiated o-methyl and o-ethyl benzamides with imines mediated by (-)-sparteine. Enantioselective synthesis of tetrahydroisoquinolin-1-ones.

The first asymmetric synthesis of tetrahydroisoquinolin-1-ones using a (-)-sparteine-mediated lateral metalation-imine addition sequence to furnish 3-phenyl tetrahydroisoquinolinones 3a with enantioselectivities up to 81% ee is described (Scheme 4). For amide 7b, imine addition products 10 and 11 have been obtained with high diastereoselectivities (91-97% de) and enantioselectivities (91-98% ee) (Scheme 8).

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PubMed2001

Asymmetric synthesis of cis-1,2-dialkenyl-substituted cyclopentanes via (-)-sparteine-mediated lithiation and cycloalkylation of a 9-chloro-2,7-nonadienyl carbamate.

Herein we report our comprehensive results in enantioselective cyclopentane synthesis via stereogenic allyllithium compounds. The described cycloalkylation reaction starts with a (-)-sparteine-mediated asymmetric deprotonation of the 2,7-alkadienyl carbamate 7e and leads to the enantioenriched (80% ee) and diastereomerically pure (dr = 99:1) cis-1,2-divinyl-cyclopentane 8, by a subsequent cyclization and elimination of lithium chloride. The reaction mechanism has been investigated by silylation and lithiodestannylation experiments and was found to represent a completely regioselective anti-S(N)'S(E)'-reaction. Trapping of the vinyllithium intermediate 12 with various electrophiles under retention of the configuration at the double bond extends the field of application for this cyclization. We also applied this reaction as the key step in the enantioselective synthesis of (+)-dihydromultifidene (17).

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PubMed2000

Sparteine-mediated asymmetric nucleophilic substitution at prochiral, sp(3)-hybridized carbon.

[reaction: see text] ++-Phenyl-1,3-dioxolanes (1) react with organolithium reagents (2), associated with (-)-sparteine, in the presence of BF(3).OEt(2) to afford chiral monosubstitution products 3. Enantioselectivity is highest if both 1 and 2 carry alkyl substituents in the ortho position. However, the enantioselectivity decreases in the case of very bulky substituents such as tert-butyl or phenyl.

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PubMed2000

C2-symmetric planar chiral ferrocene diamides by (-)-sparteine-mediated directed ortho-lithiation. Synthesis and catalytic activity

[reaction: see text] A variety of highly enantioenriched singly and doubly (4) functionalized derivatives of 1,1'-N,N,N',N'-tetraisopropylferrocenedicarboxamide 1 have been synthesized by (-)-sparteine (2)-mediated directed ortho-metalation and Pd-catalyzed cross coupling reactions. The synthetic applications of these chiral ligands in asymmetric alkylation of benzaldehyde and Pd(0)-catalyzed allylic substitution have been demonstrated.

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PubMed2002

Dibromo[(-)-sparteine-kappa2N,N']zinc(II).

In the title compound, dibromo[(6R,7S,8S,14S)-1,3,4,7,7a,8,9,10,11,13,14,14a-dodecahydro-7,14-methano-2H,6H-dipyrido[1,2-a:1',2'-e][1,5]diazocine-kappa(2)N,N']zinc(II), [ZnBr(2)(C(15)H(26)N(2))], the chiral nitrogen-chelating alkaloid (-)-L-sparteine acts as a bidentate ligand, with two bromide ligands occupying the remaining coordination sites, producing a slightly distorted tetrahedral structure. The dihedral angle between the N-Zn-N and Br-Zn-Br planes is 82.4 (1) degrees. The distortion of the tetrahedral coordination is demonstrated by the fact that the midpoint of the N...N line does not lie in the Br-Zn-Br plane, but is tilted towards one of the N atoms by 0.164 A. Similarly, the midpoint of the Br...Br line is tilted towards one of the Br atoms by 0.117 A.

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PubMed2004

Dichloro[(6R,7S,8S,14S)-(-)-sparteine-kappa(2)N,N']nickel(II).

In the title compound, [NiCl(2)(C(15)H(26)N(2))], the chiral alkaloid (6R,7S,8S,14S)-(-)-L-sparteine acts as a bidentate ligand, with two chloride ligands occupying the remaining coordination sites, producing a slightly distorted tetrahedron. The N-Ni-N plane in the title complex is twisted by 81.31 (11) degrees from the Cl-Ni-Cl plane. Other distortions of the tetrahedron are discussed.

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