3, 3-Dimethoxy-2-pyrrolidinopropene (7) is shown to be a useful intermediate for the synthesis of &formylpterin (l), 7-formylpterin (8), and 5-deaza-7-formylpterin (9). Thus, treatment of 7 with nitrosyl chloride followed by hydrolysis gives l, l-dimethoxy-3-oximino-2- propanone (3) which with aminomalononitrile (13) provides 2-amino-3-cyan~ 5 (dimethoxymethyl) pyrazine 1-oxide (la), an established precursor of 1, by way of ita ...