Alkenes Vilsmeier-Haack reaction

The classical Vilsmeier-Haack reaction - involves electrophilic substitution of a suitable carbon nucleophile with a chloromethyleneiminium salt, for example salt (1). Suitable carbon nucleophiles are generally electron-rich aromatic compounds such as V,N-dimethylaniline (2), alkene derivatives such as styrene (3) or activated methyl or methylene compounds such as 2,4,6-trinitrotoluene (4 Scheme I). These compounds (2-4) react with salt (1) giving, after loss of hydrogen chloride, the corresponding im-inium salts (5-7). Hydrolysis of iminium salt (5) affords aldehyde derivative (8) and this transformation (Ar—H - Ar—CHO) is the well-known Vilsmeier-Haack formylation reaction. Hydrolysis of iminium... 

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