Superparamagnetic Iron Oxide as an Efficient Catalyst for the One-Pot, Solvent-Free Synthesis of 5,5-Disubstituted Hexahydropyrimidines and Their Spiro Analogues

Table 3

Synthesis of bis-spiropiperidines using dimedone, aromatic amines, and formaldehyde.

Entry	R^2	Product	Time (h)	Yield (%)	m.p (°C)	Reference
1	4-Methyl	5a	3	89	196–198	[21]
2	3-Methyl	5b	3	88	186–188	[12]
3	4-Methoxy	5c	3.5	89	186–188	[21]
4	4-chloro	5d	5	73	198–200