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Elemental Analysis calcd for C27H22ClN3O4: C 66.46, H 4.54, N 8.61; found: C 66.43, H 4.56, N 8.62.
TRIS Salt Formation. Methanol (400 mL) was added to a mixture of 1 (4.0 g, 8.2 mmol) and 2-amino-2-hydroxymethylpropane-1,3-diol (TRIS, 1.0 g, 8.2 mmol). The mixture was heated to 70 °C for 0.5 h. After cooling to room temperature, the solvent was removed in vacuum. The residue was sonicated in dichloromethane (10 mL) and concentrated again. The resulting white solid was dried under vacuum overnight. The crude material was crystallized by slurring the solid residue in a 4:1 mixture of acetonitrile and methanol (5 mL). The mixture was stirred at room temperature for 24 h to give 4-((N-benzyl-8-chloro-1-methyl-1,4-dihydrochromeno- [4,3-c]pyrazole-3-carboxamido)methyl)benzoic acid TRIS salt as a white salt (3.7 g, 73% yield). Melting point: 195.6 °C. 1 H NMR (400 MHz, DMSO): δ 7.92−7.80 (m, 2H), 7.78−7.64 (m, 1H), 7.41− 7.19 (m, 8H), 7.13−7.00 (m, 1H), 5.44 (s, 2H), 5.25−5.14 (m, 2H), 4.61−4.48 (m, 2H), 4.18−4.03 (m, 3H), 3.39 (s, 7H). TRIS OH masked by water peak. LC-MS m/z: 488.0/490.0 (M+H)+ ; chlorine pattern, method 3. RT = 1.58 min. Elemental Analysis calc for C31H33ClN4O7: C 61.00, H 5.36, N 9.15; found: C 60.84, H 5.34, N 9.13.
An efficient synthetic approach for the synthesis of α-pyrones via Baeyer–Villiger-type oxidation of α-iodocyclopentenones through a catalyst- and additive-free system using air as an environmentally benign oxidant is described. The reaction exhibits excellent functional group compatibility and provides a simple and efficient protocol for the construction of highly functionalized α-pyrones under mild reaction conditions.
Catalyst- and additive-free Baeyer–Villiger-type oxidation of α-iodocyclopentenones to α-pyrones: using air as the oxidant†
An efficient synthetic approach for the synthesis of α-pyrones via Baeyer−Villiger-type oxidation of α-iodocyclopentenones through a catalyst- and additive-free system using air as an environmentally benign oxidant is described. The reaction exhibits excellent functional group compatibility and provides a simple and efficient protocol for the construction of highly functionalized α-pyrones under mild reaction conditions.
To a stirred suspension of NaH (60%, 127 mg, 3.45 mmol) in t-BuOMe (100 mL) was added 4-(trifluoromethoxy)benzyl alcohol 11 (5 mL, 34.5 mmol) dropwise by syringe at room temperature. After H2 evolution had ceased (about 5 min), the clear mixture was cooled to 0 °C. Cl3CCN (3.46 mL, 34.5 mmol) was added dropwise by syringe, and the resulting solution was stirred for 1 h. After warming to room temperature, the solution was concentrated in vacuo, and the residue was resuspended in heptane (100 mL) containing MeOH (0.14 mL, 3.45 mmol). After 10 min of stirring, the suspension was filtered through a thin bed of silica and washed with heptane. Concentration in vacuo affords the title compound as a yellow-orange liquid (11.4 g, 98%) that was used directly without further purification. Rf 0.3 (5% EtOAc/hexanes);
To a stirred solution of (R)-3-chloro-1,2-propanediol (6.61 g, 59.8 mmol) in CH2Cl2 (120 mL) was added imidazole (4.07 g, 59.8 mmol). After the reaction mixture had cooled to 0 °C, p-methoxybenzoyl chloride (10.2 g, 59.8 mmol) in CH2Cl2 (10 mL) was added dropwise via addition funnel. The resulting solution was allowed to warm to room temperature and stirred until complete consumption of starting material by thin layer chromatography (TLC). The mixture was poured into saturated aq NH4Cl (150 mL), and the aqueous layer was extracted with CH2Cl2 (3 × 100 mL). The combined organic extracts were dried (MgSO4), filtered, and concentrated in vacuo to provide chlorohydrin 10as a clear, viscous oil (11.43 g, 78%) that was used without further purification. Rf 0.3 (20% EtOAc/hexanes); ee >99% as determined by chiral SFC (see the Supporting Information);
The combined organic extracts were washed with brine, dried (Na2SO4), filtered, and concentrated. Chromatography (75% EtOAc/hexanes) followed by recrystallization (i-PrOH/hexanes) affords PA-824 (1) (2.41 g, 62%) as a crystalline solid. Mp 150−151 °C (lit.(11a) mp 149−150); Rf 0.2 (75% EtOAc/hexanes); ee >99.9% as determined by chiral SFC (see the Supporting Information);