Double 1,4-addition of malonate to 1,2-diaza-1,3-butadienes: a useful route to previously unknown symmetric and unsymmetric 1,6-dioxo-2,7-diazaspiro[4.4]nona-3,8-dienes

In the presence of sodium methoxide in tetrahydrofuran, 1,2-diaza-1,3-butadienes react with dimethyl malonate in a 2:1 molar ratio to give symmetric or unsymmetric bishydrazones that in turn produce new 1,6-dioxo-2,7-diazaspiro[4.4]nona-3,8-dienes, as a consequence of a double ring closure, on treatment with sodium methoxide in methanol.