Regio- and Diastereoselective Samarium-Mediated Allylic Benzoate Reductions

Abstract

ContentsGeneral Experimental Procedures S2 Diastereoselectivity analysis by 1 H NMR S54 Scheme 3 NMR analysis S55 NOESY data for compounds 17 and 18 S67-69 Compound Procedure/Characterization 1 Szostak, M. Spain, M.; Procter, D. J. J. Org. Chem. 2012, 77, 3049 S2 unless otherwise mentioned. All TLC analysis used 0.25 mm silica layer fluorescence UV254 plates. Flash chromatography: SilaCycle silica gel P60 (230-400 mesh). NMR: Spectra were recorded on a Unity Inova 500 MHz FT-NMR Spectometer in the solvents indicated; chemical shifts (δ) are given in ppm, coupling constants (J) in Hz. Determination of diasteromeric ratios were calculated using MestreNova 10.0 software (example below). The solvent signals were used as references (CDCl3: δC ≡ 77.0 ppm; residual CHCl3 in CDCl3: δH ≡ 7.26 ppm). General Experimental ProceduresProcedure A: Benzoylation of an alcohol Pyridine (2 equiv.) was added to a schlenk tube containing substrate (1 equiv.) in DCM (0.2 M relative to substrate). The mixture was then cooled to 0 o C followed by the addition of benzoyl chloride (1.2 equiv.).The reaction was allowed to warm to room temperature for fifteen hours, quenched with aq. NaHCO3, and extracted with DCM (3x). The combined organic extracts were dried over MgSO4, and concentrated in vacuo. Procedure B: DDQ removal of PMB protecting group. Substrate was added to a round bottom containing a 50:50 mixture of DCM:pH 7 buffer (0.1 M relative to substrate). The reaction mixture was cooled to 0 o C and stirred vigorously at which time DDQ (3 equiv.) was added portion wise over 30 min. The reaction was left to run for 1 hour, quenched with aq. NaOH (1.0 M), extracted with DCM (3x), and washed with brine. The combined organic extracts were dried over MgSO-4, and concentrated in vacuo Procedure C: SmI2 reductive elimination with H2O To a dry schlenk tube containing a solution of SmI2 in THF (0.1 M, 7 equiv.) was added degassed nano pure H2O (105 equiv.) turning the solution a deep red color. The solution was stirred for 5 min. and the substrate (1 equiv) was then added. After 30 min. the reaction was quenched with aq. NaHCO3, and extracted with EtOAc (3x). The combined organic extracts were dried over MgSO4, and concentrated in vacuo. S3 Compound 6. To a schlenk tube filled with dichloromethane (DCM) (20 mL) and Cp2ZrCl2 (0.171 g, 0.587 mmol) at -20 o C was added trimethyl aluminum (2.0 M in toluene, 5.87 mL, 11.74 mmol) dropwise resulting in a yellow solution which was stirred for 10 minutes. DI H2O (0.104 mL, 5.87 mmol) was then added dropwise turning the solution a darker shade of yellow which was then stirred for another 10 min. The reaction was then warmed to room temperature for ten min and then cooled to 0 o C. Phenyl acetylene (0.644 mL, 5.87 mmol) was added dropwise and the solution was stirred for 40 min at 0 o C. Aldehyde 5 (1.0 g, 4.7 mmol) was then added dropwise and the mixture stirred for 1 h at 0 o C. The reaction was quenched slowly with H2O (1.0 mL) and then aq. HCl (1.0 M, 10 mL), extracted with DCM (2 x 20 mL), and washed...

Hydroxyl-Directed Regio- and Diastereoselective Allylic Sulfone Reductions with [Sm(H2O)n]I2

“…The existing stereocenter directs the facial selectivity of intramolecular protonation by a samarium-bound water. This model is consistent with the stereochemistry of the newly formed asymmetric carbon atom (*) for the major diastereomers obtained. − …”

“…Purification by flash column chromatography on silica (4:1 hexanes:EtOAc) gave 2e (0.090 g, 66%) as an oil and a 1. 4 Hz, 3H), 0.93 (d, J = 6.5 Hz, 6H), 0.91 (d, J = 6.7 Hz, 3H), 0.91 (d, J = 6.9 Hz, 3H). Spectral data for the major diastereomer: 13 (E)-5-Phenylhex-3-en-2-ol (3a).…”

“…Our group has been exploring a samarium diiodide (SmI 2 ) mediated elimination/isomerization process for asymmetric carbon atom synthesis. − We have found that upon treatment with SmI 2 and water ([Sm­(H 2 O) n ]­I 2 ), , substrates of type A are transformed into alkene products B in high yield and in some cases high diastereoselectivity (up to 90:10; Scheme ). The reaction is thought to proceed through a chelated organosamarium intermediate ( Sm–I ), formed upon the reduction and loss of the benzoyl ester (OBz).…”

“…This model is consistent with the stereochemistry of the newly formed asymmetric carbon atom (*) for the major diastereomers obtained. 4 − 6 …”