Intramolecular Dehydro Diels-Alder Reactions of Diarylacetylenes: Synthesis of 5H-Benzo[j]phenanthridine and 6H-Naphtho[2,3-c]chromene Skeletons

Abstract

Intramolecular dehydro Diels-Alder reactions of aniline and phenol diarylacetylene derivatives lead to the formation of 5H-benzo[j]phenanthridine and 6H-naphtho[2,3-c]chromene skeletons.

Key words

arenynes - aromatic polycycles - benzo[j]phenanth­ridines - dehydro Diels-Alder reactions - naphtho[2,3-c]chromenes

References

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9

All new compounds gave satisfactory analytical and spectroscopic data.

10

All unsuccessful attempts were esterifications of 2-(2-phenyl-1-ethynyl)phenol under different conditions: a) propiolic acid, DCC, DMAP; b) propiolic acid, SOCl₂; c) methyl propiolate, p-TsOH, 90 °C.

12

Thermolysis of a mesitylene solution of 15 for 20 h at 215 °C gave a 15% yield of naphtho[2,3-c]chromene.

14

Typical experimental procedure: A solution of 16 (70 mg, 0.26 mmol) in toluene (10 mL) was heated in a sealed tube at 160 °C for 10 h. After removal of the solvent, the crude residue was purified by column chromatography on silica gel using a mixture of hexanes/EtOAc (7:1) as eluent, giving 50 mg (71%) of 19 as a pale yellow oil. ¹H NMR (250 MHz, CD₃Cl) δ: 8.16 (s, 1 H, ArH), 7.94-7.87 (m, 2 H, ArH), 7.72-7.64 (m, 1 H, ArH), 7.55-7.46 (m, 2 H, ArH), 7.31 (td, J = 7.2 Hz, 1.6 Hz, 1 H, ArH), 7.13 (td, J = 8.5 Hz, 1.3 Hz, 1 H, ArH), 7.05 (dd, J = 7.9 Hz, 1.3 Hz, 1 H, ArH), 5.15 (s, 2 H, CH ₂), 2.71 (s, 3 H, CH ₃). ¹³C NMR + DEPT (62.83 MHz, CD₃Cl) δ: 206.1 (CO), 155.0 (C), 136.1 (C), 133.2 (C), 129.9 (CH), 128.8 (CH), 128.2 (C), 128.0 (C), 127.0 (CH), 126.6 (CH), 126.2 (C), 124.3 (CH), 123.8 (CH), 122.5 (CH), 122.4 (C), 122.1 (CH), 117.6 (CH), 66.1 (CH₂), 33.1 (CH₃). EM m/z (%): 274 (M⁺, 100), 273 (45), 231 (61), 202 (53). HRMS C₁₉H₁₄O₂: calcd 274.09938, found 274.09940.