NOVELTY - Preparation of a substituted phenyl compound (I), comprises (i) reaction of a benzenediazonium compound (II) with (E)-but-2-enal (III) in the presence of a palladium source and an alcohol compound (IV), where the palladium (Pd) source is Pd(0) on a support, Pd(0) complex and/or Pd(II) complex.    USE - (I) are useful for preparing the compounds (NBEA) and (I-red-aid), which are useful as fragrance, odorant, aroma or flavor agent. The ester compound (I-p-ester) is useful as an intermediate for preparation of antineoplastic antifolates, folate anitmetabolites or (S)-2-(4-(2-(2-amino-4-oxo-4,7-dihydro-3H-pyrrolo(2,3-d)pyrimidin-5-yl)-ethyl)-benzoylamino)-pentanedioic acid (all claimed). The process is useful for the preparation of 4,4-dialkoxy-1-buten-1-ylarenes from crotonaldehyde and aryldiazonium salts. No biological data given.    ADVANTAGE - The production process does not need vinyl tin precursors. The process is characterized by lower cost and less process steps, avoids toxic substances and reduces waste.    DETAILED DESCRIPTION - Preparation of a substituted phenyl compound of formula (I), comprises reaction of a benzenediazonium compound of formula (II) with (E)-but-2-enal (III) in the presence of a palladium source and an alcohol compound of formula (R4-OH) (IV), where the palladium (Pd) source is Pd(0) on a support, Pd(0) complex and/or Pd(II) complex.    R1-R3 = H, 1-4C alkyl, 1-4C alkoxy, halo, CF3, NO2, SO2CH3, OCF3, OCHF2, C(O)OR5, CN, C(O)N(R7)R8, C(O)R10 or phenyl (optionally substituted by 1-3 groups comprising 1-4C alkyl, halo, NO2, CF3, OCF3, OCHF2, CN or C(O)R11);    R5 = 1-8C alkyl, CH2CF3 or CH(CF3)2;    R7, R8 = 1-10C alkyl;    R10 = 1-10C alkyl, CF3 or phenyl (optionally substituted by 1-3 groups comprising 1-4C alkyl, halo, NO2, CF3, OCF3, OCHF2 or CN);    R11 = 1-10C alkyl or CF3;    R4 = 1-4C alkyl or (CH2)2-OCH3; and    X = BF4 , PF6 , Cl, Br, H2PO4 or HSO4.    INDEPENDENT CLAIMS are included for:    (1) n-buten-1-al (NBEA) products;    (2) substituted phenyl compounds of formula (I-red); and    (3) substituted 4-phenyl-butyraldehyde compounds of formula (I-red-aid).