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1,3-Dipolar Cycloadditions of Diazoalkanes to Activated Sulfoxides: Influence of Lewis Acids

Author/s
García Ruano, J. L.; Peromingo, M. T.; Alonso, M.; Fraile, A.; Martín, M. R. and Tito, A.
Año de edición
2005
Referencia completa

J. Org. Chem. 2005, 70, 8942-8947. DOI: 10.1021/jo051574v

Resumen

The reactions of diazomethane and diazoethane with (S)-3-p-tolylsulfinylfuran-2(5H)-one (3) and its 4-methyl derivative (4) have been studied. The sulfinyl group was able to completely control the ð-facial selectivity of all these reactions, which decreased when the polarity of the solvent increased and could be inverted in the presence of Lewis acids, Yb(OTf)3 being the most efficient catalyst. This behavior made possible the stereodivergent synthesis of diastereoisomeric pyrazolines in almost quantitative yields and de’s higher than 98%. The endo/exo selectivity was also complete in reactions of 3 with diazoethane, whereas 4 afforded an easily separable 1:1 mixture of diastereoisomers. Steric factors accounts for the endo/exo selectivity, whereas electrostatic interactions must also be considered to explain the facial selectivity.

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