Glyme s. 1,2-Dimethoxyethane

Glycosyl migration, review 20, 258 suppl. 26 N-Glycosyl - 26, 316 Glyme s. 1,2-Dimethoxyethane s. a. Diglyme... 

In the reaction of 1-hexene to give 56 as the major product, an essential component is easy to overlook. The ether solvent is important, and the solvent glytne is commonly used. The formal name of glyme is 1,2-dimethoxyethane and it has the structure CH3OCH2CH2OCH3. If borane is simply mixed with 1-hexene with no solvent, no reaction occru-s unless the mixture is heated to about 180-200°C. In ether solvents, however, the reaction occurs rapidly at ambient temperatures (i.e., room temperatru-e). In fact, ethers catalyze the reaction of borane with an alkene and, although the ether structure does not appear in the product, the ether is not simply a solvent. This is probably because the oxygen atom of an ether is a Lewis base (remember the ate complex formed from borane and diethyl ether) and reacts with diborane to form a highly reactive complex that reacts with the alkene. All reactions of alkenes with borane in this chapter will use an ether solvent. 

In order to overcome these difficulties, work is being done on the electrolyte, experimenting with the use of ether molecules such as 1,3-dioxolane (DIOX) or tetrahydrofiirane (THF). Solvents such as glyme, whose general formula is given in Figure 9.10 (such as 1,2-dimethoxyethane (DME)), are also commonly used in Li-S batteries. However, these solvents flounder because of their property of solubilization of hthium polysulfides. 

Acyloins (la) [29,30] and bis-silylated derivatives of their enediols (lb) [31] have been demonstrated to be useful acyl anion equivalents (RCO ) and have been employed in an indirect but facile way for the preparation of ketones (3) (Equation 7.1). The hydroxy ketones (2), which are the key intermediates in this method, have been prepared by the reaction of acyloins (la) with organic halides in the presence of sodium hydroxide in dimethyl sulfoxide [29, 30] according to the Hein s procedure [32] or using sodium hydride in 1,2-dimethoxyethane (DME) (glyme) [33]. They also have been prepared by the alkylation of lithium enedi-olates of acyloins prepared from the corresponding lb and methyllithium [31]. These reactions proceed with C-alkylation however, the reaction conditions employed are quite basic which would limit substrate choice. 

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