Highly Efficient Synthesis of Pyrimidines under Microwave-assisted Conditions

Abstract

Microwave irradiation of an amidine and alkynone in acetonitrile at 120 °C gives 2,4-disubstituted and 2,4,6-trisubsti­tuted pyrimidines in very high yield.

Key words

pyrimidines - microwave synthesis - heterocycles

References

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17

In a typical experimental procedure, a mixture of 1-phenyl-2-propyn-1-one 1a [12] (0.13 g, 1.0 mmol), benzamidine hydrochloride salt 2a·HCl (0.19 g, 1.2 mmol) and sodium carbonate (0.25 g, 2.4 mmol) in acetonitrile (5 ml) was irradiated for 40 min in a self-tunable CEM microwave synthesizer at 120 °C (initial power 90 W) and then allowed to cool. The solution was filtered and evaporated in vacuo to give 2,4-diphenylpyrimidine 3a (0.23 g, 99%) as a yellow solid, mp 72-73 °C (lit. [19] mp 71 °C); IR (nujol)/cm^-1: 1563; ¹H NMR (CDCl₃; 400 MHz) δ (ppm) 8.73 (1 H, d, J = 4 Hz, 6-H), 8.50 (2 H, m, o-PhH), 8.13 (2 H, m, o-PhH), 7.49 (1 H, d, J = 4 Hz, 5-H), 7.43 (6 H, m, m,p-PhH); ¹³C NMR (CDCl₃; 100 MHz) δ (ppm) 164.6 (C), 164.0 (C), 157.8 (CH), 137.8 (C), 136.9 (C), 131.1 (CH), 130.8 (CH), 129.0 (CH), 128.7 (CH), 128.6 (CH), 127.3 (CH), 114.6 (CH); m/z (APcI) 233 (MH⁺, 100%).

18

Compounds demonstrated spectroscopic properties that were in agreement with literature data.