Hydroxy-1,2,2-triphenylethyl Acetate

Stereoselective Aldol Reactions. The (R)- and (S)-2-hydroxy-1,2,2-triphenylethyl acetates (HYTRA) offer a simple soludon for a stereoselecdve aldol addition of a-unsubstituted enolates. When a suspension of HYTRA is treated in THF with 2 equiv of Lithium Diisopropylamide, a clear soludon of the enolate forms (eq 1). Subsequent dilution with 2-methylbutane followed by the addition of 2-methylpropanal affords predominantly the (R,R)-diastereomeric adduct. Alkaline hydrolysis not only delivers (/ )-3-hydroxy-4-methylpentanoic acid in 86-94% ee but also liberates the optically pure auxiliary reagent (/ )-1,2,2-triphenylethane-1,2-diol, which can be removed and reused (eq 1). -  

The diastereoselectivity has been enhanced by a transmetalation of the lithium enolate with Magnesium Bromide or Magnesium Iodide prior to the addition of benzaldehyde (eq 2).  

On the other hand, enantiomeric excesses up to 94% are reached even at —78 °C, provided that Lithium Hexamethyldisilazide (LH-MDS) (3 equiv) is used for deprotonation instead of LDA (2 equiv) (eq 3).  

Related Reagents. Boron Triiodide R)-2-r-Butyl-6-methyl-4ff-1,3-dioxin-4-one (5)-4-Benzyl-2-oxazolidinone (/ ,/ )-1,2-Diphenyl-1,2-diaminoethane A dV -Bis[3,5-bis- 

10-Dicyclohexylsulfonamidoisobomeol Diisopinocampheyl-boron Trifluoromethanesulfonate a-Methyltoluene-2,a-sultam 1,1,2-Triphenyl-1,2-ethanediol. 

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R)-(+)-1,1,2-Triphenyl-1,2-ethanediol is available from methyl3 and ethyl4 (R)-(-)-mandelate by treatment with phenylmagnesium bromide. The synthesis of (R)-(+)-2-hydroxy-1,2,2-triphenylethyl acetate [(R)-HYTRA] has been reported previously by the submitters.5 6 (S)-(-)-2-Hydroxy-1,2,2-triphenylethyl acetate is available according to this procedure starting from the enantiomeric methyl (S)-(+)-mandelate or (S)-(+)-... 

STEREOSELECTIVE ALDOL REACTION OF DOUBLY DEPROTONATED (RM+)-2-HYDROXY-1,2,2-TRIPHENYLETHYL ACETATE (HYTRA) (R)-3-HYDROXY-4-METHYLPENTANOIC ACID (Pentanoic acid, 3-hydroxy-4-methyl-, (R)-)... 

R)-(+)-2-Hydroxy-1,2,2-triphenylethyl acetate [(R)-HYTRA], To a mechanically stirred solution of (R)-(+)-1,1,2-triphenyl-1,2-ethanediol (35.0 g. 0.121 mol, Note 1) and acetic anhydride (17.1 mL, 0.181 mol, 1.5 eq, Note 2) in anhydrous acetonitrile (500 mL, Note 3) at room temperature under nitrogen is added a solution of scandium(lll) trifluoromethanesulfonate (1.23 g, 2.5 mmol, 2 mol%, Note 4) in anhydrous acetonitrile (125 mL) over approximately 35 min (Note 5). After about 8 min a white precipitate begins to appear, and the resulting mixture is stirred at room temperature under nitrogen for a total of 3 hr. The solid is filtered, washed with acetonitrile (2 x 25 mL), and dried under vacuum at 40°C overnight to afford (R)-(+)-2-hydroxy-1,2,2-triphenylethyl acetate (35.42 g, 0.107 mol, 88%) as a white solid (Note 6). 

Related Reagents. 10-Dicyclohexylsulfonamidoisobomeol 2-Hydroxy-1,2,2-triphenylethyl Acetate (4.S, 5iS )-4-Methoxy-methyl-2-methyl-5-phenyl-2-oxazoline ot-Methyltoluene-2,ot-sultam (5)-4-Benzyl-2-oxazolidinone. 

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