A Novel Method for the Synthesis of 2,3-Benzo-1,3a,6a-triazapentalenes through Pummerer-Type Reactions of γ-(Benzotriazol-1-yl)allylic Sulfoxides

Treatment of 1-(arylmethyl)benzotriazoles 1 with nBuLi in THF at −78 °C, followed by addition of 1-aryl-2-chloroethanones, gave diastereomeric mixtures of 1-[(aryl)(benzotriazol-1-yl)methyl]oxiranes 2. Treatment of 2 with nBuLi in THF at −78 °C, followed by acidification, afforded a mixture of (E)- and (Z)-allylic alcohols 3, which were converted into 1,2-disubstituted 2-(alkyl- or aryl)-1-(benzotriazol-1-yl)-3-sulfanylpropenes 5 via the corresponding allylic chlorides 4. Oxidation of sulfides 5 by mCPBA in CH2Cl2 at room temperature, followed by treatment with trifluoroacetic anhydride (TFAA) at room temperature, gave the title compounds in good yields. It was found that treatment of the title compounds with Raney-Ni in EtOH under hydrogen at reflux gave 2-(pyrazol-1-yl)aniline derivatives in excellent yields.