The condensation of active methylene reagents with salicylaldehyde:: Novel synthesis of chromene, azaanthracene, pyrano[3,4-c]chromene and chromeno[3,4-c]pyridine derivatives

On heating of the cyanoacetic acid cyclopentylidene hydrazide I with salicylaldehyde in the presence of bases the azaanthracene derivative 6 was formed. Also, reaction of 3 with malononitrile and ketones 10a,b afforded the pyrano[3,4-c]chromene 9 and chromeno[3,4-c]pyridine 11 respectively. A mechanism for these reactions is proposed.