Process for the production of substituted cyclopropanals.

The invention relates to a process for the preparation of the formula CyclopropancarbaldehydenwhereinR 'is C1-C4Alkyl or benzyl, characterized in thata) a tetrahydrofuran of formulawhereinX is halogen andR2 optionally halogen-substituted C1-C10Alkyl optionally substituted by halogen, C1-C4Alkyl or C1-C4. -alkoxy C3-C6Cycloalkyl, or optionally substituted by halogen, C1-C4Alkyl, C1-C4Alkoxy, nitro, cyano-substituted phenyl or benzyl, with a halogenating agent to give a 1,2,4-Trihalogenbutylehter of formulawhereinX is halogen andR2 optionally halogen-substituted C1-C10Alkyl optionally substituted by halogen, C1-C4Alkyl or C1-C4-alkoxy-Substituted C3-C6Cycloalkyl, or optionally substituted by halogen, C1-C4Alkyl, C1-C4Alkoxy, nitro. Cyano-substituted phenyl or benzyl, reacted andb) then the compound of formula III with an aqueous bisulfite solution to a bisulfite adduct of the formulawhereinX is halogen andY is a cation equivalent of an alkali or alkaline earth metal ion, reacted andc) then in the presence of a base, with a thiolate of formula R1-Se Z9 (V) whereinR 'is C1-C4-alkyl Or benzyl andZ is a cation equivalent of an alkali or alkaline earth metal ion, cyclized to a cyclopropanecarbaldehyde of formula I, as well as the individual process steps a), b) andc) and combinations of a) + b) and b) + c) and the new intermediates of formula III and IV.