Dialkylphosphonates add in a 1,2 fashion to the C = N bond in 5,5-dimethyl-3-thiozolines 2 to form dialkyl rac-(4-thiazolidinyl)phosphonates 3a – e. Upon hydrolysis of 3arac-(1-amino-2-mercapto-2-methylpropyl)phosphonic acid (4a), the phosphonic acid analog of penicillamine (1), is formed.