Redal

In the fine chemical industry, reduction of carbonyl groups mainly relies on the use of complex metal hydrides sodium dihydrobis-(2-methoxyethoxy)-aluminate, commercialized as RedAl or Vitride is one of the most used (4). 

He made both starting materials from esters of the corresponding aryl acetic acids 53 and 56 by reduction and substitution (in the case of the phosphonium salt). This gave added flexibility as either component can be used as the phosphonium salt 55 or the aldehyde 54. He used the unusual reducing agent REDAL [NaAlH2(0CH2CH20Me)2] instead of DIB AL to make the aldehyde 54. 

Scheme 4 depicts the remainder of our total synthesis. The acid (5) was subjected to RedAl reduction to give the hydroxymethyl intermediate (6) in 99 % yield, which was then protected as the terf-butyldiphenylsilyl ether (7) under standard conditions (96 %). Silicon-mediated fragmentation of the acetonide (7) was carried out under Lewis acid-mediated conditions (BF, OEtj) to fiimish allylic alcohol (8) in 96 % yield. Sharpless epoxidation provided (9), followed by a diastereosclective diimide reduction of the remaining oleHn, to give the epoxyalcohol (10) in satisfactory yield, uid as exclusively one diastereoisomer. 

The effect of the catalyst chemical nature is demonstrated using two catalysts, sodium hydride, NaH, and sodium )is(2-metoxy-ethoxy)aluminium hydride, RedAl , which react with L6 giving rise to two lactamate anions with different nucleophilicity. The... 

Sodium bis(2-methoxyethoxy(aluminum hydride)) (Redal-H) is an excellent reagent for reducing propargylic alcohols to allylic alcohols. Reviews (a) Seyden-Penne, J. Reductions by the Alumino- and Borohydrides in organic Synthesis Wiley-VCH NewYork, 1997, 2" edition, (b) Mdlek, J. Org. React. 1985, 34, 1-317. 

To a solution of the propargylic alcohol (7.7 g, 40 mmol) in ether (150 mL) was added Redal-H (18 mL of a 65% solution in toluene, 60 mmol) at 0 °C, and the mixture was stirred for 2 h at 0 °C. The mixture was then stirred at room temperature for 3 h, and the reaction was quenched with saturated potassium sodium tartrate solution at 0 °C. After separation of the mixture, the aqueous washes were extracted with EtOAc (four times). The combined organic layers were washed with brine, dried (magnesium sulfate), and concentrated in vacuo. The crude product was purified by silica gel column chromatography (EtOAc/hexanes 20%, 25%) to give 7.3 g (94%) of the /ran.y-allylic alcohol as a yellow oil. 

Redal reduction was regioselective in affording a preponderence of 1,3 diols over 1,2 diols (9 1). Acylation and chromatographic purification produced pure... 

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