Magnesium hydride reduction

Lithium hydride is perhaps the most usehil of the other metal hydrides. The principal limitation is poor solubiUty, which essentially limits reaction media to such solvents as dioxane and dibutyl ether. Sodium hydride, which is too insoluble to function efficiently in solvents, is an effective reducing agent for the production of silane when dissolved in a LiCl—KCl eutectic at 348°C (63—65). Magnesium hydride has also been shown to be effective in the reduction of chloro- and fluorosilanes in solvent systems (66) and eutectic melts (67). 

Neopentyl alcohol has been made by lithium aluminum hydride reduction of trimethylacetic acid and by treating ferf-butyl-magnesium chloride with methyl formate. ... 

Another hydride, magnesium hydride prepared in situ from lithium aluminum hydride and diethylmagnesium, reduced terminal alkynes to 1-alkenes in 78-98% yields in the presence of cuprous iodide or cuprous r rt-butoxide, and 2-hexyne to pure cij-2-hexene in 80-81% yields [///]. Reduction of alkynes by lithium aluminum hydride in the presence of transition metals gave alkenes with small amounts of alkanes. Internal acetylenes were reduced predominantly but not exclusively to cis alkenes [377,378]. 

The reaction of alkyl dihalogenoacetate magnesium enolates with 2,3-isopropylidene-D-glyceraldehyde affords the expected /3-hydroxy-a-dihalogenoesters . The erythro isomer is obtained with isopropyl dichloroacetate magnesium enolate. This result is in agreement with theoretical models. 2-Deoxy-pentono-1,4-lactones are obtained after removal of the halogen atom by either Raney nickel or tributyltin hydride reduction (equation 89). 

Since the hemiacetal 3, can now readily be prepared from cheap commercially available starting materials (vide supra, Eq. (1))7), this reaction constitutes a convenient source of 1-vinylcyclopropanols. Otherwise, the 1-ethynyl-cyclopropanols 9, also easily available from 3 or from its magnesium salt 10 (vide supra, Eq. (4) and (6) underwent either lithium aluminium hydride reduction in refluxing THF to lead exclusively to the E-1-vinylcyclopropanols 69 or reduction with dicyclopentadienyl-titanium hydride in ether at 0.°C, prepared from isobutylmagnesium halides and a catalytic amount of dicyclopentadienyl titanium dichloride (r -CjH TiCk), to yield exclusively the Z isomer 70, Eq. (22) 15,39). 

Alternative routes to unimolecular reduction include hydrogen abstraction by ketyls (see (ii)), Meerwein-Ponndorf reduction by alkoxides [A]f and reduction by a reactive form of magnesium hydride... 

The availability of trimethylsilane in larger amounts and reproducible quality was our key to silane surfactant chemistry [6]. The successful reduction of chlorotrimethylsilane with hydrides, such as magnesium hydride in etheral solution, gave the corresponding hydrogen silane in excellent yields. Further transformations with a,P-unsaturated olefins carrying a hydrophilic moiety opened up exciting new opportunities for the synthesis of Si-surfactants (Fig. 3) [7]. 

Reduction. This hydride reduces alkyl iodides to the alkane in quantitative yield at 25° (24 hours) alkyl bromides, alkyl chlorides, and aryl iodides are relatively inert under these conditions. It reduces enones predominantly by 1,2-addition. It reduces 4-t-butylcyclohexanone quantitatively the ratio of cis- to trans-alcohol is 83 17. When magnesium hydride is used for this reduction more of the trans-alcohol is obtained, the ratio being 24 76. 

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