Tetrahydropyranyl protecting group. II. 3-Bromo-2-(tetrahydropyran-2-yloxy)propene, a masked acetonyl bromide

Abstract

It is shown that the sodium hydride (in dimethyl formamide) induced elimination of hydrogen bromide from 1,3-dibromo-2-(tetrahydropyran-2-yloxy)propane (3) can be considered to result in the in situ formation of 3-bromo-2-(tetrahydropyran-2-yloxy)propene (4). When generated in this manner, 4 was shown to function as a masked acetonyl bromide of considerable utility. Under similar conditions, 1,3-dibromo-2-methoxypropane was assumed to produce 3-bromo-2-methoxypropene, which also was shown to be a useful masked acetonyl bromide.The pyrolytic elimination of methanol from bromoacetone dimethyl ketal was shown to produce a 1:1 mixture of the two possible isomeric enol ethers, rather than pure 3-bromo-2-methoxypropene as stated in the literature (2).