Bromomagnesium diisopropylamide

Krafft and Holton have found that bromomagnesium diisopropylamide (BMDA) in an ethereal solution may be used in conjunction with the system TMSCl/EtsN/HMPA to prepare thermodynamic silylenol ethers. Reaction times of 8-12 h at 25 °C are required for the complete conversion to trimethylsilyl enolates (equation 67). 

Aldol condensation. The final step in a synthesis of the tricyclic taxane ring system involves an intramolecular aldol condensation of 2. Treatment with the usual bases results in a retro Michael reaction, but the desired cyclization to 3 can be effected in 90% yield by use of bromomagnesium diisopropylamide (1) or isopropylcyclohexylamide. The hydroxy ketone undergoes retroaldolization in the presence of mild acids or bases, but can be reduced and stored as the corresponding stable diol. 

Preparative Methods conveniently prepared - by reaction of the magnesium enolate of r-butyl acetate (readily made with Bromomagnesium Diisopropylamide) with (-)-(lR,2S,5R)-Menthyl (S)-p-Toluenesulfinate (eq 1). It was also made in 91% yield by reacting a solution of Lithium Diisopropylamide with (R)-(+)-methyl p-tolyl sulfoxide and 7-butyl carbonate (eq 2). It should be noted that asymmetric oxidation of 7-butyl 2- p-tolylsulfinyl)acetate with a modified Sharpless reagent gave a... 

Reaction with Carbonyl Compounds. Although seldom used in comparison with bromomagnesium diisopropylamide, bromomagnesium hexamethyldisilazide has the unique feature of high solubility in organic solvents. 

Bromomagnesium hexamethyldisilazide and bromomagnesium diisopropylamide were the most effective of several magnesium bases examined for selective formation of the more substituted silyl enol ether fromketones (eq 1). Less-hindered ketones gave mainly aldol products. ... 

Under the conditions used for the generation of silyl enol ethers of symmetrical ketones, unsymmetrical ketones give mixtures of structurally isomeric enol ethers, with the predominant product being the more substituted enol ether (eq 20). Highly hindered bases, such as Lithium Diisopropylamide (LDA), favor formation of the kinetic, less substituted silyl enol ether, whereas Bromomagnesium Diisopropylamide (BMDA) generates the more substituted, thermodynamic silyl enol ether. A combination of TMSCl/SodiMOT Iodide has also been used to form silyl enol ethers of simple aldehydes and ketones as well as from a, i-unsaturated aldehydes and ketones. Additionally, treatment of a-halo ketones with Zinc, TMSCI, and TMEDA in ether provides... 

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