Competitive azomethine ylide cycloaddition and carbonyl-ene reaction in the treatment of 4-(alk-2-enyl)amino-2-formylpyr-2(2H)-ones with sarcosine ethyl ester

The thermal reaction of 4-(alk-2-enyl)amino-2-formyl-2)2 H)-pyrones 4 with sarcosine ethyl ester (2) gave two isomeric pyrrol[3,4-c]pyrano[4,3-d]pyrid ines 5 and 6, arising from the endo-cycloaddition of the resulting S- and W - shaped azomethine ylides, and [1,3]oxazines 8 via the carbonyl-ene reacti on of pyrones 4 depending on the reaction conditions.