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Butenolide anions reactions with acetals

The aldehyde was then used in an aldol reaction with the anion from 3-isopropylbut-2-enolide. [The lactone was prepared in the following way bromination of 3-methyl-2-butanone under kinetic conditions (-15 °C) afforded the 1-bromo derivative. The bromine was displaced by acetate on refluxing a solution in acetone with anhydrous KOAc. Reaction of the resulting keto-acetate with the anion from triethylphosphonoacetate afforded the desired butenolide in 55% yield.] The anion was generated in tetrahydrofuran from the butenolide and lithium diisopropylamide and was cooled to -78 °C before addition of the aldehyde. The temperature was maintained below -70 °C for 5h and the reaction was quenched with ammonium chloride at this temperature. Under these conditions (kinetic) the 22R23R intermediate (3) was obtained in 65% yield (26). [Pg.41]

Attempted reaction of (52), (53), or the 5a-5,6,22,23-tetrahydro-derivative with methoxymethylenetriphenylphosphorane was unsuccessful, although pregnenolone acetate, or better its tetrahydropyranyl ether, afforded the vinyl ether, as (59). Wittig reaction of either the 5a- or A -diacetates (60) or (61) with the anion of diethylcyanomethylphosphonate gave good yields of unsaturated nitrile (62) in the absence of an acidic work-up, or the imino-lactone hydrochloride (63) in the presence of acid, which could be converted in good yield to the butenolide (64). [Pg.415]

A remarkable kinetic resolution was observed recently by Feringa and coworkers when 2-silyloxyfuran was reacted with the racemic unsymmetrical allylic substrate 86, catalyzed by the palladium complex of Trost s ligand (/ ,/ )-14, as illustrated in Scheme 5.28. The acetate anion liberated upon oxidative addition of palladium(O) is assumed to cleave the silyl protecting group, so that the enolate anion forms aside from TMSOAc. After allylic alkylation of that enolate, double bond migration leads to butenolide (R)-87 isolated in 47%, if the reaction was run with 52% conversion. Not only the product 87 but also the recovered acetate... [Pg.283]


See other pages where Butenolide anions reactions with acetals is mentioned: [Pg.215]    [Pg.256]    [Pg.314]    [Pg.115]    [Pg.319]    [Pg.331]   


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2- butenolide

3,4 -3 -butenolid

Acetals reactions with

Acetate anion

Acetates reactions with

Butenolide anions

Butenolides

Reactions with anions

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