A Green, Expeditious, One-Pot Synthesis of 3, 4-Dihydropyrimidin-2(1H)-ones Using a Mixture of Phosphorus Pentoxide-Methanesulfonic Acid at Ambient Temperature

Table 3

Expeditious synthesis of 3,4-dihydropyrimidin-2(1H)-ones (4a–4u) using Eaton’s reagent under solvent-free conditions^a.

Entry	R1	R2	X	Time (min)	Yield^b (%)	Melting point (^°C)
						Found	Reported [reference]
4 a	C6H5	C2H5	O	5	94	202–204	202–204 [12]
4b	4-F–C6H4	C2H5	O	5	90	184–186	182-183 [31]
4c	4-NO2–C6H4	C2H5	O	10	89	210–212	207-208 [12]
4d	2,3-Cl2–C6H3	C2H5	O	10	91	248–250	—
4e	2,6-Cl2–C6H3	C2H5	O	10	91	284–286	280–283 [42]
4f	3-NO2–C6H4	C2H5	O	10	89	226–228	226-227 [11]
4g	2,4-Cl2–C6H3	C2H5	O	10	89	252–254	249–251 [11]
4h	4-Br–C6H4	C2H5	O	5	92	216–218	213–215 [43]
4i	4-OH–C6H4	C2H5	O	15	75	226–228	227-228 [11]
4j	2-Cl–C6H4	C2H5	O	5	85	218–220	216–219 [11]
4k	4-Cl–C6H4	C2H5	O	5	85	214–218	213–215 [12]
4l	4-OCH3–C6H4	C2H5	O	15	86	202–204	201-202 [12]
4m	2-Cl–C6H4	CH3	O	5	90	224–228	224-225 [11]
4n	4-F–C6H4	CH3	O	5	86	208–210	—
4o	C6H5	CH3	O	5	92	212–214	213-214 [11]
4p	4-Cl–C6H4	CH3	O	5	90	210–212	204–207 [11]
4q	C6H5	C2H5	S	5	96	208–209	208-209 [12]
4r	3-NO2–C6H4	C2H5	S	5	80	202–204	202–204 [44]
4s	4-CH3–C6H4	C2H5	S	10	77	194–198	191–193 [45]
4t	4-OH–C6H4	C2H5	S	15	80	196-198	195–197 [44]
4u	4-OCH3–C6H4	C2H5	S	15	77	140–142	140 [46]

^aAldehyde (1 mmol), ethyl/methylacetoacetate (1 mmol), urea/thiourea (1.5 mmol), Eaton’s reagent (2 mmol), solvent-free, RT.
^bYield refers to isolated product.