4 Benzyloxy 2 butanone

A. 4-Benzyloxy-2-butanone. A 100-mL, three-necked, round-bottomed flask is equipped with a magnetic stirring bar, a condenser mounted with a nitrogen inlet, and a pressure-equalizing dropping funnel (Note 1). The flask is charged with 4.40 g (0.050 mol) of 4-hydroxy-2-butanone (Note 2), 50 mL of dry toluene (Note... 

The effect of the steric bulk of the hydride reducing agent has been examined in the case of 3-benzyloxy-2-butanone.135 The ratio of chelation-controlled product increased with the steric bulk of the reductant. This is presumably due to amplification of the steric effect of the methyl group in the chelated TS as the reductant becomes more sterically demanding. In these reactions, the degree of chelation control was also enhanced by use of CH2C12 as a cosolvent. 

The Reformatsky reactions of methyl or ethyl bromoacetate with 4-acetoxy-,2,24 4-benzyloxy-,2 4-tetrahydropyranyloxy-,2 4-chloro-,8 and 4,4-dimethoxy-2-butanone1418 have been carried out. The adducts were converted to mevalonolactone by hydrolysis and, in the case of the acetal reactant, by appropriate reduction and oxidation procedures. The same Reformatsky-type syntheses of mevalonolactone have also been performed using the lithium and magnesium carbanions of acetate esters5,19 25 26 and the dianion of acetic acid28,27 instead of the usual zinc reagent. The intramolecular Reformatsky reaction of 4-(bromoacetoxy)-2-butanone gives mevalonolactone directly.28 A related route to mevalonolactone involves boron trifluoride-catalyzed cycloaddition of ketene to 4-acetoxy-2-butanone followed by hydrolysis.183... 

An a-benzyloxy group was found to cause rate acceleration of more than 100, relative to a nonchelating a-trimethylsiloxy group. On the other hand, a 4-benzyloxy group in 2-butanone ((i-substitution) caused only a 20% rate increase. 

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