Natural Hydroxyapatite: Green Catalyst for the Synthesis of Pyrroles, Inhibitors of Corrosion

Table 3

Multicomponent synthesis of pyrroles by various substrates^a.

Entry	R1	R2	R3	R4	Products	Yields^b (%)
1	Me	Ph	H	Me	1c	48 [30]
2	Me	CH3CH (Ph)	H	Me	1d	90
3	Me	Ph-CH2	H	Me	1e	74 [31]
4	Me	CH3CHCH3	H	Me	1f	44
5	Me	Ph	Cl	Me	1g	50
6	Me	Ph-CH2	Cl	Me	1h	67 [25]
7	Me	CH3CH (Ph)	Cl	Me	1i	44
8	Me	CH3CHCH3	Cl	Me	1j	41
9	Me	Ph	Me	Me	1k	63
10	Me	Ph-CH2	Me	Me	1l	77
11	Me	CH3CH (Ph)	Me	Me	1m	64
12	Me	Ph-CH2	1-Naphthyl	Me	1n	37
13	Me	CH3CH (Ph)	1-Naphthyl	Me	1o	39
14	Me	CH3CHCH3	1-Naphthyl	Me	1p	90
15	OEt	Ph-CH2	Me	H	1q	29
16	OEt	Ph	H	H	1r	30
17	OEt	Ph-CH2	H	H	1s	43
18	OEt	CH3CH (Ph)	H	H	1t	41
19	OEt	CH3CHCH3	H	H	1u	29

^aReactions were carried out using aldehyde (2.5 mmol), amine (2.5 mmol), and 1,3-dicarbonyl compounds (2.5 mmol) to nitromethane (5 mmol), HAp (S/C) = 60, T = 60°C, t = 24 h. ^bIsolated yield.