| 摘要 |
A novel process for the manufacture of a gamma -halotiglic aldehyde HalH2C-CH=C(CH3)-CHO [I], wherein Hal signifies chlorine or bromine, comprises haloalkoxylating a 1-alkoxy-2-methyl-1,3-butadiene H2C=CH-C (CH3)=CH-OR1 [II], wherein R1 signifies C1-4-alkyl, using a particular halogenating agent in a C1-4-alkanol (R2OH) and hydrolyzing the thus-obtained gamma -halotiglic aldehyde dialkyl acetal HalH2C-CH=C(CH3)-CH (OR1)(OR2) [III] to the desired gamma -chloro- or gamma -bromotiglic aldehyde I. The halogenating agent used in this process is selected from an alkali metal hypochlorite, an alkali metal hypobromite, an alkaline earth metal hypochlorite, an alkaline earth metal hypobromite, tert.butyl hypochlorite, N-bromoacetamide, 1.3-dichloro-5,5-dimethylhydantoin and 1,3-dibromo-5,5-dimethylhydantoin. Further aspects of the present invention are the use of the thus manufactured gamma -halotiglic aldehyde for the production of gamma -acetoxy-tiglic aldehyde or of a Wittig aldehyde halide Hal-Ph3P+CH2-CH=C(CH3)-CHO [VII], wherein Hal signifies chlorine or bromine and Ph a process for the catalytic dealkoxylation of the 1,1,3-trialkoxy-2-methyl-butane CH3-CH(ORl)-CH(CH3)-CH(OR1)2 [VI] to the corresponding 1-alkoxy-2-methyl-1,3-butadiene II in the gas phase using an aluminium silicate of medium specific surface as the catalyst. The products I, gamma -acetoxy-tiglic aldehyde and VII are known, important intermediates for the production of various apocarotenoids and diapocarotenoids as well as of Vitamin A.
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