The present invention is directed to an efficient process for the manufacture of (E)-4-N,N-dialkylamino crotonic acid in HX salt form of formula I wherein R1 and R2 independently denote C1-3-alkyl groups and X− denotes an acid anion, such as the chloride, bromide, tosylate, mesylate or trifluoroacetate anion, with high quality, and a process for synthesis of EGFR tyrosine kinase inhibitors with heterocyclic quinazoline, quinoline or pyrimidopyrimidine core structure, using the acid addition salt I and activated derivatives thereof as intermediates.