Gas-Phase Pyrolysis in Organic Synthesis: Rapid Green Synthesis of 4-Quinolinones

Abstract

Gas-phase pyrolysis of aminomethylene Meldrum’s acid derivatives gave quinolinones and/or amines depending on the ­nature of arylamino moiety. Effect of substituent on reaction rate and nature of pyrolysis products supports the suggested intramolecular nucleophilic substitution reaction via initially formed keteneamine intermediate.

Key words

Meldrum’s acid - pyrolysis - 4-quinolinones

References and Notes

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12

Static Pyrolysis of 8-j
The substrate (0.2 g) was introduced in the Pyrex reaction tube (12 cm length and 1.5 cm internal diameter). The tube was sealed under vacuum (0.02 m bar) and placed in the pyrolyzer for 900 s at 300 °C. The content of the tube was then separated by preparative high-performance liquid chromatography (HPLC) and was analyzed by ¹H NMR, ¹³C NMR, IR and GC-MS. Relative and percent yields were determined from NMR.

13

Flash Vacuum Pyrolysis of 8a-j The sample was volatilized from a tube in a Buchi Kugelrohr oven through a 30 × 2.5 cm horizontal-fused quartz tube and was heated externally by a cabolite Eurotherm tube furnace MTF-12/38A to 600 °C. The products were collected in a U-shaped trap cooled in liquid nitrogen. The whole system was maintained at a pressure of 10^-2 Torr by an Edwards Model E2M5 high-capacity rotary oil pump, the pressure being measured by a Pirani gauge situated between the cold trap and pump. Under these condition the contact time in the hot zone was estimated to be 10 ms. Products collected in the U-shaped trap were analyzed by ¹H NMR, ¹³C NMR, IR and GC-MS. Relative and percent yields were determined from NMR.
Compounds 11a,c,d,f-h,j-n, 16, and 17 has been reported earlier and proved to be identical with products obtained here. [19-27]

14

6-Methyl-1 H -quinolin-4-one ( 11b)
Mp 240-242 °C. IR (KBr): 3050 (NH), 1625 (CO) cm^-1. LC-MS: m/z (%) = 159 (100) [M⁺]. ¹H NMR (400 MHz, DMSO): δ = 2.39 (s, 3 H, CH₃), 6.0 (d, 1 H, J = 7.2 Hz, quinoline-H3), 7.45 (d, 1 H, quinoline-H8), 7.48 (d, 1 H, quinoline-H7), 7.86 (d, 1 H, J = 7.2 Hz, quinoline-H2), 8.31 (s, 1 H, quinoline-H5), 11.72 (br s, 1 H, D₂O exchangeable, NH). ¹³C NMR (DMSO, 100 MHz): δ = 21.55, 109.09, 119.18, 124.70, 125.96, 134.31, 134.57, 138.67, 140.50, 178.48. DEPT 135: δ = 21.55, 109.09, 119.18, 124.70, 125.96, 134.57, 140.50.

15

7-Bromo-1 H -quinolin-4-one ( 11e)
Mp 242-244 °C. LC-MS: m/z = 225 [M + 1]. ¹H NMR (400 MHz, DMSO): δ = 6.04 (d, 1 H, H3, J = 7.37 Hz), 7.52 (d, 1 H, J = 8.56 Hz), 7.74 (s, 1 H, H-5), 7.82 (d, 1 H, J = 7.37 Hz, H2), 8 (d, 1 H, J = 8.56 Hz, H6), 11.22 (br, 1 H, NH). ¹³C NMR (100 MHz, DMSO): δ = 111.5, 120.4, 123.2, 126, 128.4, 132.7, 141, 143.4, 177.4.

16

5-Bromo-1 H -quinolin-4-one ( 11i)
Mp 234-236 °C. IR (KBr): 1645 (CO) cm^-1. LC-MS: m/z = 225 [M + 1]. ¹H NMR (400 MHz, DMSO): δ = 6.06 (d, 1 H, H3, J = 7.24 Hz), 7.41-7.47 (m, 3 H, ArH), 7.93 (d, 1 H, J = 7.24 Hz, H-2), 11.18 (br, 1 H, NH). ¹³C NMR (75 MHz, DMSO): δ = 110.3, 119.5, 121.5, 125.6, 127.2, 130.6, 139.3, 142, 177.

18

Pyrazino[1,2- a ]pyrimidin-4-one ( 19) Mp 178-180 °C. IR (KBr): 1692 (CO) cm^-1. LC-MS: m/z = 148 [M + 1]. ¹H NMR (400 MHz, DMSO): δ = 6.67 (d, 1 H, J = 6.44 Hz, pyrimidine-H), 8.19 (d, 1 H, J = 4.64 Hz, pyrazine-H), 8.41 (d, 1 H, J = 6.44 Hz, pyrimidine-H), 8.73 (d, 1 H, J = 4.64 Hz, pyrazine-H), 9.13 (s, 1 H, pyrazine-H). ¹³C NMR (75 MHz, DMSO): δ = 109.6, 118.2, 133.0, 145.8, 154.2, 155.9, 156.8. DEPT 135: δ = 109.6, 118.2, 133.0, 154.2, 155.9. Anal. Calcd for C₇H₅N₃O (147.14): C, 57.14; H, 3.43; N, 28.56. Found: C, 57.53; H, 3.62; N, 28.83.