Beta-amino-alpha-cyanoacrylates and their use as herbicides

beta-Amino-alpha-Cyanoacrylates of formula I where the variables have the following meanings: R is n-alkyl, n-alkenyl or alkoxyalkyl; R ,R are alkyl, which may be partially or fully halogenated and/or may carry a substituent from the group consisting of cyano, alkoxy, haloalkoxy, alkylthio, haloalkylthio, C -C -alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl and haloalkylsulfonyl, are alkenyl or alkynyl; or R and R together with the carbon atom to which they are attached form a cycloalkyl ring in which one or two nonadjacent CH groups may be replaced by oxygen or sulfur, and where the cycloalkyl ring may be substituted by halogen or alkyl; R is hydrogen, halogen, cyano or alkyl, where the substituents R , R and R or two of the radicals R , R and R are not simultaneously methyl, and their agriculturally useful salts, processes and intermediates for their preparation; and the use of these compounds or of compositions comprising these compounds for controlling undesirable plants are described.