Hydrides organomagnesiums

The addition of mild nucleophiles occurs preferentially in a (as described below) but with hydride, organomagnesium, or organolithium reagents addition in y can also be observed, leading to isolable y-pyrans. 

The reduction of carbonyl compounds by reaction with hydride reagents (H -) and the Grignard addition by reaction with organomagnesium halides (R - +MgBr) are examples of nucleophilic carbonyl addition reactions. What analogous product do you think might result from reaction of cyanide ion with a ketone ... 

An efficient primary amine synthesis via iV-diisobutylaluminium imines has been described. A cyanide R CN (R1 = Bu, CsHn, Ph, 2-furyl or 2-thienyl) is treated with diisobutylaluminium hydride and the product is converted into the amine by reaction with an organomagnesium or organolithium compound R2M (R2 = Bu, t-Bu, allyl or benzyl)... 

Detailed reviews on the structures of organomagnesium compounds and the constitution of their solutions have been published [D, 1, 2]. These references, especially the first two, also cover alkylmagnesium hydrides, amides, alkoxides and thiolates. However, while all of these compounds are of intrinsic interest, they are little used in synthesis. 

The hydrosilane reagents used, where available, were obtained from commercial suppliers such as Pierce Chemical (Rockford, 111.), Peninsular Chem Research (Gainesville, Fla.), and Matheson, Coleman and Bell (Norwood, Ohio). Others were synthesized by the lithium aluminum hydride or deuteride (Alfa Chemical, Beverly, Mass.) reduction of appropriate organic chloro- or fluorosilane, either purchased from the above-mentioned sources or synthesized by conventional routes involving organomagnesium or -lithium condensations with halosilanes. All such compounds were at least 98% pure as determined by vapor-phase chromatography (VPC). Structural identity was established by molecular analysis, infrared, and NMR spectroscopy where necessary. 

Organomagnesium hydrides (RMgH) with THF solvation are stable. They form dimeric and oligomeric structures associated through bridging hydrides. 

Lactone synthesis. This Ti(II) complex can serve as catalyst for hydro-magnesiation of allylic or homoallylic alcohols, prepared by addition of vinyl- or allyl-Grignard reagents to ketones. Ethylmagnesium bromide is used as the source of magnesium hydride. The carbonylation of the organomagnesium intermediate results in a -y- or a 5-lactone (equation I). 

Aluminum alkyls, although inconvenient to handle because of their spontaneous inflammability, are powerful reducing agents and are applied to the synthesis of transition-metal hydrides . They, and the organomagnesium halide reagents to be discussed in 1.10.8.4, function by initial alkylation of the transition metal (e.g., for EtjAl) ... 

As a secondary organomagnesium halide reagent, cyclohexylmagnesium bromide may also be useful for the synthesis of metal hydrides ... 

---