Pyrazolones spiro

The class of 2-amino-4H-pyrans has been known for several decades. The first representatives 1 and 2 are from the late 1950s to the early 1960s. Spiro-conjugated pyranopyrazole 1 was obtained in studies on pyrazolone dyestuffs (56ACS587), while pyranopyranone 2 served as a precursor for the blood anticoagulant warfarin (62JOC3086). 

A three-component reaction of piperidin-4-ones 246, pyrazolones 194b, and malononitrile 27a represents a convenient approach to spiro 247 (02OL423) (Scheme 94). 

---