Alkyl derivatives aluminum reagents

The oxazaborolidines are easily prepared by heating ephedrine with borane dimethyl sulfide or the appropriate boronate ester. The aluminum reagent C is obtained by mixing ephedrine and trimethylaluminum. Borolidinc A is superior to its methyl derivative B and to the aluminum analog C. The diastereomeric borolidine obtained from borane and (S,S)-pseu-doephedrine failed to show any cnantioselectivity25. A variety of aromatic aldehydes can be enantioselectively alkylated in the presence of A, however, with heptanal the enantioselectivity is poor25. 

In addition to their reactions with trlmethylsilyl enol ethers, (propargyl1um)Co2(C0)g complexes react with a variety of other mild carbon nucleophiles including activated aromatic compounds, g-dicarbonyl compounds, other enol derivatives (enol acetates and ketones directly), allylsilanes, and alkyl- and alkynyl-aluminum reagents. These reactions provide a flexible means to introduce the synthetically versatile propargyl function. Key features of propargylations using these complexes are 1) ready... 

Actually, the titanium carbene LXVIII (not as stable as the chromium derivative) is usually generated in situ by stoichiometric reactions of titanium complexes with alkyls of aluminum or magnesium (typically, Tebbe s reagent LXVII ) [107]. 

A first aluminum derivative is complexed between the two oxygen atoms of 57, which have to be in an appropriate configuration to allow this chelation. A second aluminum reagent is then complexed by the oxygen bearing the most available electron lone pair. This second complexation directs the reaction of de-O-alkylation, and rationalizes the observed regioselectivity leading to 58 as the sole product (Scheme 9.27). The mechanism involves two aluminum derivatives, one as a Lewis acid, which activates the alkyl ether, the other as a hydride donor, which reacts with the activated position [63]. 

In the general context of donor/acceptor formulation, the carbonyl derivatives (especially ketones) are utilized as electron acceptors in a wide variety of reactions such as additions with Grignard reagents, alkyl metals, enolates (aldol condensation), hydroxide (Cannizzaro reaction), alkoxides (Meerwein-Pondorff-Verley reduction), thiolates, phenolates, etc. reduction to alcohols with lithium aluminum hydride, sodium borohydride, trialkyltin hydrides, etc. and cyloadditions with electron-rich olefins (Paterno-Buchi reaction), acetylenes, and dienes.46... 

Cobalt hydrocarbonyl, diborane, and aluminum hydrides add, I think, to all of these carbonyl compounds. Of course, there is the well known Grignard reagent and the alkyllithium additions to carbonyl compounds. Aluminum alkyls add, and we could have listed all the other alkali metal alkyls. Recent work has shown that the tin alkoxides add readily to all these derivatives, and similarly, a tin amide adds to most of these carbonyl compounds. 

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