“On-Water” Catalyst-Free Ecofriendly Synthesis of the Hantzsch Dihydropyridines

Table 1

Ammonium acetate-mediated “on-water” synthesis of the Hantzsch 1,4-Dihydropyridines.

Entry^a	RCHO	Time (min)	Isolated yield of dihydropyridine (%)	Observed M.p. (^∘C)	Literature M.p. (^∘C)
1		70	89	155	157 [10]
2		75	91	139	140 [11]
3		65	89	136	135–137 [22]
4		75	80	229-230	230–232 [21]
5		65	93	145	146 [10]
6		65	96	125	126 [10]
7		120	92	163	163 [10]
8		90	84	129	129 [11]
9		90	85	162-163	163 [10]
10		90	80	192-193	192–194 [46]
11		70	89	145-146	147 [10]
12		80	86	142	—
13		150^b	70	Viscous oil	—
14		180^c	75	182	183 [36]
15		120^b	71	Viscous oil [10, 13]	—

^aAldehyde : EAA : ammonium acetate = 1 : 2 : 1.3.
^bReactions in water : ethanol = 1 : 1.
^cReaction temperature = 30^∘C.