Regioselective synthesis of imines (2-N-amine-3-N-(phenylmethylene)-5-pyridine) in water under microwave irradiation

Figures & data

Table 1. Reaction times, yields, temperature and method for the synthesis of 2-N-amine-3-N-(2-hydroxy-phenylmethylene)-5-bromo-pyridine

Entry	Solvent	Time (min)	Method	Temp. (°C)	Yield (%)^a
1	Toluene^b	60	Reflux	100	52
2	Toluene^b	60	Microwave	100	62
3	Toluene^b	60	Ultrasound	40	58
4	Water	60	Reflux	100	98
5	Water	60	Microwave	100	90
6	Water	60	Ultrasound	40	96
7	Water	20	Microwave	100	98
8	Water	10	Microwave	100	95

^a Yield isolated imine.

^b Dried solvent.

Table 2. Reaction times and yields for compounds 3a–n obtained using water and MW irradiation

Compound	Substituents						Yield (%)
	X1	X2	R1	R2	R3	R4
3a^a	N	C	Br	OH	H	H	95
3b^a	N	C	Br	H	OCH3	OH	85
3c^a	N	C	Br	H	H	OH	86
3d^a	N	C	H	H	OH	OH	87
3e^a	N	N	Br	OCH3	–	OCH3	64
3f^a	N	C	Br	H	–O–CH2–O–		78
3g^a	N	C	Br	H	H	CH3	84
3h^a	N	C	Br	2-methxycinnamal			85
3i^a	N	C	Br	H	H	CF3	78
3j^a	N	C	H	H	–O–CH2–O–		64
3k^a	N	C	Br	H	OH	OH	86
3l^b	N	C	Br	H	H	H	54
3m^a	N	C	Br	H	H	NO2	74
3n^c	CH	C	CO2H	–	H	H	78

^a Reaction time: 10 min.

^b Reaction time: 7 min.

^c Reaction time: 30 min.

Figure 1. Isomers that can be formed from this class of compounds.

Figure 2. NOESY spectra of 3m isomer A and 3m isomer B and their possible conformations (for the best visualization of the content, see electronic supplementary information, page S20 and S22).

Figure 3. ORTEP plots of compounds 3b, 3b′, 3c, 3e, 3f, 3g, 3h, and 3l.