Stabilization of carbanions by polarization of alkyl groups on nonadjacent atoms

Abstract

and NMR was obtained. All attempts at crystallization were unsuccessful: IR (CHClg) 3700-3300 (br), 2950-2800 (br), 1725 cm"1; NMR (CDClg), composite of Table I and Table II; EIMS m/e (relative intensity) 317 (M+, 0.6), 148 (10), 139 (15), 138 (89), 135 (22), 105 (17), 94 (42), 93 (100), 80 (24), 77 (17), 57 (44); CIMS m/e (relative intensity) 318 (M+ + 1,83), 138 (100); high-resolution MS, molecular ion m/e 317.1524, caled, for CyHggNCh 317.1628. 9-0-[(±)-2-Hydroxy-2-phenylbutyryl]retronecine . To a solution of 0.974 g (3.07 mmol) of 2 in 3.75 mL of ethanol was added 1.0 mL of 30% hydrogen peroxide. This mixture was kept at 4 °C in a refrigerator for 2 days. The excess peroxide was destroyed by the addition of Mn02. The solution was then filtered and the solvent removed in vacuo, leaving a colorless viscous oil. The presence of N-oxide was determined by using a Mattocks test.18 TLC on silica gel with 10% methanol/CHClg as the solvent showed a single spot at R¡ 0.47 as compared to Rf 0.59 for the free alkaloid. This difference in R¡ of 0.1 is typical for pyrrolizidine alkaloid iV-oxides:1 NMR (CDClg) characteristic peaks 0.85 (br t, 3 H, J = 5.0 Hz), 4.69 (br s, 2 H), 5.51 (br s, 1 H), 7.29 (br m, 3 H), 7.47 (br m, 2 H); EIMS m/e (relative intensity) 165 (1), 155 (4), 138 (22), 136 (22), 135 (100), 117 (23), 106 (12), 105 (49), 104 (12); CIMS m/e (relative intensity) 318 ( + 1, 36), 300 (11), 163 (16), 139 (13), 138 (100), 136 (14), 135 (20). 9-0-[(S)-(+)-2-Hydroxy-2-phenylbutyryl]retronecine (5).A solution of 1,1 '-carbonyldiimidazole (0.218 g, 1.35 mmol) and (+) -2-hydroxy-2-phenylbutyric acid (0.212 g, 1.29 mmol) in 15 mL of dry CHClg under an argon atmosphere was stirred for 15 (18) Mattocks, A. R. Anal. Chem. 1967, 39, 443. min to allow for the complete evolution of C02. To this was then added retronecine (0.2058 g, 1.33 mmol), and the solution was stirred for 20 h at room temperature. The CHClg was washed with 10 mL of saturated NaHCOg. The aqueous layer was extracted with 10 mL of CHClg, and the combined CHC13 extracts were dried (MgSOJ, filtered, and reduced in vacuo, leaving 0.3844 g (94%) of a colorless viscous oil: NMR (CDClg) see Table I; IR (CHClg) 3650-3400, 3100-2800,1725 cm"1; [ ]20^+ 4.6°(c 2.19, MeOH); EIMS m/e (relative intensity) 317 (M+, 2), 139 (18), 138 (95), 136 (14), 135 (32), 105 (11), 94 (41), 93 (100), 80 (26);CIMS m/e (relative intensity) 318 (M+ + 1,44), 300 (11), 139 (13), 138 (100), 136 (16), 135 (20); high-resolution MS, molecular ion m/e 317.1588, caled, for Ci8H23N04 317.1628. 9-0-[(JZ)-(-)-2-Hydroxy-2-phenylbutyryl]retronecine (6). The reaction was carried out exactly as described for 5 except that (-)-2-hydroxy-2-phenylbutyric acid was used: NMR (CDClg) see Table II; [a]20^+ 6.0°(c 3.16, MeOH); EIMS exactly the same as for 5; high-resolution MS, molecular ion m/e 317.1660, caled, for C18H23N04 317.1628.Registry No. (±)-2a, 81340-07-0; 3, 480-85-3; 4, 315-22-0; (+)-(S)-5,81340-08-1; (-)-fi-6, 81370-87-8; (+)-2-hydroxy-2-phenylbutyric acid, 24256-91-5; (-)-2-hydroxy-2-phe...

Iron‐Catalyzed Arylation of Aromatic Ketones and Aldehydes Mediated by Organosilanes

“…Total reaction time 7 h, after which the washed crude product was purified by flash chromatography with hexane to yield a colorless oil, yield 94 % (472 mg), R f = 0.47 (dichloromethane/hexane, 1:3). Characterization data is consistent with that published previously 31…”

Steric hindrance effects on bimolecular coupling rate constants of carbon-centered radicals

“…9-(2-Methylphenyl)fluorene, 29 9-(2,4,6-trimethyl-phenyl)fluorene, 29 9-phenylxanthene 28 and 9-(2-methylphenyl)xanthene 30 were synthesized by Grignard reaction of the appropriate aryl bromide [bromobenzene (Aldrich, 99%), 2-bromotoluene (Aldrich, 99%) or 2-bromomestylene (Aldrich, 99%)] and an aromatic cyclic ketone [9-fluorenone (Aldrich, 98%) or 9-xanthenone (Aldrich, 99%)] followed by reduction of the alcohol with a mixture of iodine, acetic acid and hypophosphorous acid. 29 Mass spectra and meltingpoints [28][29][30] confirmed the identities of the products. All manipulations of solutions were done by syringe (Series 1000, Hamilton, Reno, NV, USA) under argon passed through an oxygen trap (RGP 125-R1, Labclear, Oakland, CA, USA) and a gas drying unit (26800, Drierite, Xenia, OH, USA).…”

Enantioselective Synthesis of Benzyl tert‐Butyl Sulfoxides

“…The combined extracts were dried with magnesium sulfate and concentrated to dryness. Purification by silica gel chromatography (pentane/EtOAc, 3:1) afforded the following: (i) an inseparable mixture of ( tert ‐butylthio)methylbenzene and bis( tert ‐butylthio)methylbenzene40 and (ii) a mixture of diastereomeric dithioacetal monosulfoxides 8 as a white solid. 1 H NMR (400 MHz, CDCl 3 ): δ = 1.12 [s, 9 H, C(C H 3 ) 3 ], 1.20 [s, 9 H, C(C H 3 ) 3 ], 1.31 [s, 9 H, C(C H 3 ) 3 ], 1.36 [s, 9 H, C(C H 3 ) 3 ], 4.83 (s, 1 H, C H Ar), 4.88 (s, 1 H, C H Ar), 7.26–7.44 (m, 10 H, Ar) ppm.…”