1,3-dipolar cycloaddition of diazoalkanes to (S)-(+)-3-[(4-methylphenyl)sulfinyl]-5,6-dihydropyran-2-one. Synthesis of optically pure cyclopropanes by denitrogenation of sulfinyl and sulfonyl pyrazolines

The addition of diazomethane and diazoethane to enantiopure (S)-(+)-3-[(methylphenyl)sulfinyl]-5,6-dihydropyran-2-one has produced the corresponding pyrazolines with almost complete [pi]-facial selectivity. The results are improved starting from sulfonyl pyrazolines, which has produced pure 3-oxabicyclo[4.1.0] heptan-2-ones.