Magnesium carbonyl hydride reactions with

The additional carbon atom required for building the five-membered ring D is then added by means of methyl-magnesium bromide (16-4). The ester at future C15 is reduced to a carbinol by reaction with lithium aluminum hydride. Swern oxidation (dimethyl sulfoxide and oxalyl chloride) next serves to oxidize each of the two resulting hydroxyl groups to carbonyl functions (16-5). Dieckmann-like base-catalyzed condensation then closes the five-membered ring... 

A nickel hydride complex, NiHCl(diphenylphosphinoethane), catalyses the tandem isomerization-aldolization reaction of allylic alcohols with aldehydes.156 The atom- (g) efficient process proceeds at or below ambient temperature with low catalyst loading, and works well even for bulky aldehydes. Magnesium bromide acts as a co-catalyst, and mechanistic investigations suggest that a free enol is formed, which then adds to the aldehyde in a hydroxyl-carbonyl-ene -type reaction. 

R)-Malic acid can be selectively protected as a dioxolanone (904). Treatment of 904 with excess methyl magnesium iodide affords lactone 905 as the result of a completely regiose-lective reaction of Grignard reagent with the dioxolanone carbonyl followed by lactonization (Scheme 133) [201]. Reduction of the lactone with lithium aluminum hydride gives triol 906, which is converted to iodoacetonide 907 (OH OTs I). This intermediate is used to supply the chiral side chain for the steroid 24,25-dihydroxycholecalciferol. 

Reactions of Fused Azepines. The morphanthridene derivative (40) undergoes an interesting rearrangement to (42) when treated with primary amines the reaction involves a transamidation which converts (41) into (42). Reversal, with concurrent reduction of the carbonyl, is induced by lithium aluminium hydride. The diarylethylene-type double-bond in some dibenz-azepines and -oxepines can be reduced conveniently and in high yield, using magnesium in methanol. 

Although reduction of ketones with alkali metals, for example, sodium (Na°) in ethanol (CH3CH2OH), to the corresponding alcohol, as already noted, has been replaced with complex hydrides, a minor product in the original reaction, the result of coupling two ketones at their respective carbonyl carbons, was occasionally found on workup of the reaction mixture. The diol (a pinacol) thus formed could be made the major product if the reaction was carried out with magnesium (Mg°) or amalgamated aluminum (Al-Hg) instead of sodium (Na°). The process, which doubtlessly involves a series of one-electron transfer reactions, is shown in Equation 9.21. 

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