A new method has been developed for the enantioselective synthesis of highly functionalised cyclopentanes bearing up to three stereogenic centres with very high stereoselectivity. This one-potprocess combines an enantioselective organocatalytic Michael addition with a highly diastereoselective [3+2]-cycloaddition-fragmentation step.
The use of platinumcomplexes as catalysts for allylic substitution has been studied. A variety of different complexescatalyse the reaction, and several substrates have been tested. In the alkylation of mono(alkyl)-substituted allylic acetates, regioselectivity is highly dependent on ligand choice. By using tricyclohexylphosphine as the ligand, almost complete formation of branched products is observed
Enantioselective Molybdenum-Catalyzed Allylic Alkylation Using Chiral Bisoxazoline Ligands
作者:Frank Glorius、Andreas Pfaltz
DOI:10.1021/ol990602r
日期:1999.7.1
[GRAPHICS]A series of chiral C-2-symmetric bisoxazolines with trans-1,2-diaminocyclohexane backbones was synthesized. In View of the promising results obtained by Trost with analogous bispyridine ligands, we tested our new ligands in the enantioselective molybdenum-catalyzed allylic alkylation of 1- and 3-monosubstituted allylic substrates, Enantiomeric excesses of up to 98% and branched/linear ratios of up to 11:1 were obtained with (E)-3-(n-alkyl)allyl carbonates. (E)-3-Phenoxyallyl acetate gave a branched/linear ratio of >20:1 and an ee of 98%.
Use of Tricyclohexylphosphine To Control Regiochemistry in Palladium-Catalyzed Allylic Alkylation
作者:A. John Blacker、Matthew L. Clarke、Michael S. Loft、Jonathan M. J. Williams
DOI:10.1021/ol9911268
日期:1999.12.1
[GRAPHICS]Tricyclohexylphosphine, Cy3P, in conjuction with [(C3H5)PdCl](2) catalyzes allylic alkylation of terminal allylic acetates with high regioselectivity toward branched products, which is in contrast to most other palladium catalysts. Other ligands, even those of similar basicity or bulkiness, did not show the same regioselectivity. Alkylation of 1,4-diacetoxy-2-butene gave predominantly branched products which had not been observed previously.