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Mentioned methods-
Dropwise addition of reagents
Reaction quenching
Liquid liquid separation
Flash chromatography.
The reaction is a three step mechanism so when adding in previous mixtures, it is important to do so dripwise as to let the reaction to occur slowly. The there were several workup techniques used. Reaction quenching to stop any further reacting to occur, liquid- liquid separation to separate organic and aqueous layers of a reaction. Lastly, flash chromatography was used to separate the 2 different stereo configurations of the prouct.
Materials
Step 1: N-sulfonyl pyrimidine- this is one of the starting materials of the reaction. (10a)
Lithium bis(trimethylsilyl)amide- Is a strong non-nucleophilic base.
Tetrahydrofuran- Used as the solvent because it has a large liquid range and it is quite polar.
Step 2- Trimethyl phosphite – This reagent is used as desulfurization agent when added into step 3 of the mechanism.
Wilkinson catalyst {[RhCl(PPh3)2)]} – This is used as a catalyst that enables the Sn2 reaction by partially replacing the oxygen molecule, preparing a more reactive leaving group to undergo the reaction.
Tetrahydrofuran- Used as the solvent because it has a large liquid range and it is quite polar.
Step 3: Cyclic carbonate- this is the second starting material of the reaction (13) created in the previous reaction.
Tetrahydrofuran- Used as the solvent because it has a large liquid range and it is quite polar.
Workup- NH4Cl- used to quench the reaction
Diethyl ether- used to separate the organic and aqueous layers.
MgSO4- Used to dry the organic layer Ethyl acetate and hexanes- solvents for flash chromatography
Amination addiuct (14a)- product with conserved stereochem.
Reaction protocol for 10a to 14b.
Trimethyl phosphate (0.24 mL, 2.05 mmol) was added directly to the red suspension of the Wilkinson’s catalyst (450g, 0.51 mmol) in anhydrous tetrahyfrofuran (10 mL). The reaction was run under a atmosphere of argon and the reaction mixture was stirred at room temperature for about 10 minutes until a yellow homogeneous solution was created.
In another flask, lithium bis(trimethylsilyl)amide (10.7 mL, 10.7 mmol, 1.0 M solution in tetrahyfrofuran) was added dropwise to the N-sulfonyl pyrimidine (10a)(3.73g, 9.74mmol) in anhydrous tetrahyfrofuran (30mL) at room temperature, allowing the anion to form over about 20 minutes.
The catalyst solution and catalytic carbonate (13) (1.24g, 4.87 mmol) in anhydrous tetrahyfrofuran (10mL) were sequentially added using a Teflon cannula to the nucleophile. The resulting reaction mixture was heated at 30°C for about 4 hours.
The reaction mixture was then quenched with saturated aq NH4Cl solution (40mL) and separated between diethyl ether and saturated aq NH4Cl solution. The aqueous layer was washed with diethyl ether and the organic layer was dried using MgSO4. This was filtered and concentrated in vacuo until a crude oil. The oil was then purified using flash chromatography (eluating with 25-60% ethyl acetate/ hexanes) furnished the amination adduct (14a) (2.46 g, 84%) as a pale yellow oil.