Beilstein J. Org. Chem.2008,4, No. 18, doi:10.3762/bjoc.4.18
, Shanghai 201620, China 10.3762/bjoc.4.18 Abstract We present a mechanistic investigation of Pd-catalyzed allylicsubstitution of cyclic gem-difluorinated carbonates 1 and 4, previously employed in the synthesis of 3',3'-difluoro-2'-hydroxymethyl-4',5'-unsaturated carbocyclic nucleosides in 17 steps. The
allylicsubstitution, in which the regioselectivity was reversed from that of nonfluorinated substrates. This reversed regioselectivity caused by fluorine interests us greatly. Herein, we present a mechanistic investigation of Pd-catalyzed allylicsubstitution of cyclic gem-difluorinated carbonates
our knowledge, the effect of gem-difluoromethylene group on Pd-catalyzed cyclic allylicsubstitution has never been addressed so far. The regioselectivity was totally different from those of nonfluorinated substrates [18].
Unexpected and specific regioselectivity of Pd-catalytic asymmetric reactions
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Graphical Abstract
Scheme 1:
Pd-catalyzed allylic substitution of the gem-difluorinated allylic carbonates 1 and 4.
Beilstein J. Org. Chem.2006,2, No. 7, doi:10.1186/1860-5397-2-7
-ligands (Table 1).
Conclusion
Besides P, N-bidentate FENOP ligands, monodentate BIFOP ligands can be employed successfully in Pd-catalyzed allylicsubstitution of 1-phenyl-2-propenyl acetate with dimethylmalonate. Surprisingly, the halogen phosphites BIFOP-Cl and BIFOP-Br are stable towards nucleophiles
extrapolated energies: BIFOP-H-re: -1025.01553 H, BIFOP-H-si: -1025.01466 H. The by 0.5 kcal mol-1 slightly preferred re-addition of the NH3 model nucleophile corresponds to the experimental S-alkylation product.
Pd-catalyzed allylicsubstitution with unsymmetrical substrates (Nu = dimethylmalonate, Nf = OAc
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Graphical Abstract
Scheme 1:
Pd-catalyzed allylic substitution with unsymmetrical substrates (Nu = dimethylmalonate, Nf = OAc).