Synthesis of norisotuboflavine

A convenient approach to the canthin‐4‐one ring system: Total synthesis of the alkaloids tuboflavine and norisotuboflavine

“…Up to now several multi‐step syntheses of the alkaloids tuboflavine [11], isotuboflavine [7], norisotuboflavine [7, 12], and of unsubstituted canthin‐4‐one [7] have been published, but none of these offer overall yields higher than 1%. So these total syntheses could only serve as proofs for the structures of the alkaloids, but do not represent efficient approaches to the canthin‐4‐one ring system.…”

“…Recrystallization from CH 2 Cl 2 ‐heptane gave yellow needles, mp 217°C (lit. [10, 12]: mp 207–208°C, 216°C (acetone‐hexane)); IR: 1610, 1573, 1510, 1470, 1438, 1345, 1292, 1166 cm −1 ; 1 H NMR (CF 3 COOD) δ 9.23 (d, 1H, J = 5.9 Hz, 2‐H), 8.90 (d, 1H, J = 5.9 Hz, 1‐H), 8.82 (s, 1H, 6‐H), 8.51 (d, 1H, J = 8.0 Hz, 11‐H), 8.11 (m, 2H, 8‐H, 9‐H), 7.81 (m, 1H, 10‐H), 2.94 (q, 2H, J = 7.5 Hz, 1′‐H), 1.45 (t, 3H, J = 7.5 Hz, 2′‐H); 13 C NMR (CF 3 COOD) δ 173.5 (CO), 144.7 (C‐7a), 143.3 (C‐3a), 140.5 (C‐2), 136.5 (C‐6), 134.7 (C‐11c), 133.6 (C‐11b), 133.5 (C‐9), 127.8 (C‐10), 126.5 (C‐11), 126.4 (C‐11a), 122.4 (C‐5), 119.9 (C‐1), 112.3 (C‐8), 20.9 (C‐1′), 10.9 (C‐2′); ms (EI) m/z 248 (M + , 100), 247 (99), 192 (25), 151 (30), 91 (24); Anal. Calcd.…”

Synthesis of S-(−)-5,6-Dihydrocanthin-4-ones via a Triple Cooperative Catalysis-Mediated Domino Reaction

“…Furthermore, to establish that the water released during the imine formation induces hydrolysis in the final step, in another control experiment molecular sieves were added to the reaction of 1a and 2b, which produced 3ab in 29% yield in only 12 h. Additionally 1a was heated with 2b, pyrrolidine, and DIEA in dry toluene in the presence of H 2 18 O (97%) under inert conditions. On completion the reaction mixture was directly subjected to mass spectral analysis and displayed the presence of a mixture of 16 O-3ab (413 amu) and 18 O-3ab (415 amu), suggesting that the water released during the imine formation is used for the hydrolysis step (see the Supporting Information). To unequivocally ascertain the participation of the pyridyl nitrogen of β-carboline for the initial nucleophilic attack onto the triple a The reactions were performed using 1a (0.1 g, 0.39 mmol), 2b (86 μL, 0.47 mmol), and pyrrolidine (7.0 μL, 0.08 mmol) in PhMe (5.0 mL).…”

New approaches to the synthesis of canthin-4-one alkaloids and synthetic analogues

“…Multiplicities are abbreviated as follows: s¼singlet, d¼doublet, t¼triplet, m¼multiplet. Signal assignments were carried out based on 1 H, 13 C, DEPT, HSQC or HMQC, HMBC and COSY spectra. Mass spectra (MS) were run by chemical impact (CI) or electron impact (EI) at 70 eV using a Hewlett Packard 5989A mass spectrometer with 59980B Particle Beam LC/MS.…”

“…Purification was accomplished by FCC using 1:1 hexaneseethyl acetate to give 80 mg of 9a (0. 32 13 C NMR (125 MHz, CDCl 3 ): d¼170.0 (C-5 0 ), 160.7 (C-3 0 ), 140.6 (C-8a), 139.2 (C-3), 132.8 (C-9a), 130.9 (C-4a), 130.0 (C-1), 129.2 (C-7), 121.8 (C-5), 120.9 (C-4b), 120.6 (C-6), 115.9 (C-4), 111.8 (C-8), 102.8 (C-4 0 ), 11.6 (CH 3 The isoxazole 9a (150 mg, 0.60 mmol) was dissolved in ethanol (12 mL), and KOH (452 mg, 8.05 mmol) and palladium (10 wt. %) on activated carbon catalyst (25 mg) were added.…”