Synthesis of 1-amino-2,2-dialkylcyclopropanecarboxylic acids from β-chloroaldimines

A variety of hydrogen cyanide adducts of β-chloroaldimines using acetone cyanohydrin were prepared. The reactive behaviour of these α-amino-γ-chloronitriles towards bases was investigated with the aim to generate 1-aminocyclopropanecarbonitriles, which are precursors for the potentially plant growth regulating 1-aminocyclopropanecarboxylic acids. The synthesis of 1-amino-2,2-dimethylcyclopropanecarboxylic acid (= 2,3-methanovaline) by a reaction sequence involving addition of hydrogen cyanide across β-chloroaldimines, ring closure to functionalized cyclopropanes and acidic hydrolysis was accomplished. Alternatively the hydrogen cyanide adducts of β-chloroaldimines were converted into α-(N-benzylidene)amino-γ-chloronitriles, which were ring closed with base and hydrolyzed to afford 1-amino-2,2-dialkylcyclopropanecarbonitriles, the latter serving again as substrates for the hydrolytic conversion into the corresponding 1-amino-2,2-dialkylcyclopropanecarboxylic acids (exemplified for 1-amino-2,2-dimethylcyclopropanecarboxylic acid).