Nitroalkanes silyl nitronate preparation

Method G Highruiri-selecdvity is also observed in the fluoride-catalyzed reacdonof silyl nitronates v/ith aldehydes. Trialkyl silyl nitronates are prepared in good yield from primary nitroalkanes by consecndve treatment v/ith iithiiim dusopropylamide and trialkylsilyl chloride at -78 C in THF. 

A series of 3-substituted-2-isoxazoles are prepared by the following simple procedure in situ conversion of nitroalkane to the silyl nitronate is followed by 1,3-dipolar cycloaddition to produce the adduct, which undergoes thermal elimination during distillation to furnish the isoxazole (Eq. 8.74). 5 Isoxazoles are useful synthetic intermediates (discussed in the chapter on nitrile oxides Section 8.2.2). Furthermore, the nucleophilic addition to the C=N bond leads to new heterocyclic systems. For example, the addition of diallyl zinc to 5-aryl-4,5-dihydroi-soxazole occurs with high diastereoselectivity (Eq. 8.75).126 Numerous synthetic applications of 1,3-dipolar cycloaddition of nitronates are summarized in work by Torssell and coworker.63a... 

A more common method for the preparation of silyl nitronates is the use of trimethylsilyl chloride (TMSCl) in the presence of a base. With triethylamine, silyl nitronates are prepared from primary nitroalkanes in moderate yields however, it is necessary to conduct the silylation in acetonitrile for good yields with secondary nitroalkanes (18,101). In several cases, this silylation has been done in the presence of the dipolarophile for both inter- and intramolecular processes, or the nitronate has been used in subsequent reactions without purification (18,22). Employment of l,8-diazabicyclo(5.4.0)undec-7-ene (DBU) as the base allows this procedure to be general for most nitroalkanes (19). 

Preparation of a-fluoro ketones or aldehydes can also be achieved by cerium ammonium nitrate oxidation of the corresponding silyl nitronates. C-acylation compounds derived from nitroalkanes can be... 

Significant improvements to the Henry reaction have been achieved by using silyl nitronates and catalytic amounts of fluoride ion or, alternatively, a,a doubly deprotonated primary nitroalkanes. Both of these procedures, discovered by the Seebach group, have proved to be useful for the stereoselective preparation of vicinal amino alcohols. 

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