Acylsilane imines

Aliphatic acylsilane imines and their salts are readily accessible (see Sections III.B.21 and III.B.2.j). Their reduction by a chiral boronate provides ready access to the corresponding chiral RSMAs.310... 

Reduction of the imine or oxime of an acylsilane provides an appropriate route to SMA derivatives, as several routes to acylsilanes are now available. This process is... 

If HMPA is used in stoichiometric amount in THF as the solvent, then substitution of the chlorine atom occurs providing the corresponding C-silylated imine, the precursor of the acylsilane pivaloylsilane. This imine can also be regarded as a good precursor of an SMA through its reduction. Reduction of the iminoylchloride into the non-silylated imine is a side reaction. 

Nitriles having at least one hydrogen on the functional carbon, react with trimethylchlorosilane under electrochemical conditions to provide a mixture of silazanes and enamines of acylsilanes. These enamines have been suggested to be formed from the isomeric ketene imine form of the nitrile. They were obtained as a mixture of Z (major) and E isomers. Treatment of the silazane-enamine mixture with trimethylchloro-silane/methanol and sodium borohydride followed by neutralization of the salt gives the corresponding RSMA.191... 

Imines of acylsilanes are excellent precursors of SMA (See Section III.B.l.m). Insertion of an isonitrile into the C-Li bond of a lithium reagent, followed by the silylation of the resulting vinyllithium derivative affords such imines.160... 

Scheldt and coworkers reported the addition of amide enolates to acylsilanes for generation of p-silylojq homoenolate equivalents 62, based on the fact that less electrophilic p-carbonyl groups disfavor the formation of cyclopropanolates 63 by internal carbanion attack (Scheme 6.30). Instead, the carbanion generated in situ can be trapped by allq l halides, aldehydes, ketones, and imines. The use of optically active amide enolates delivers p-hydroxy amides with high levels of diastereoselectivity. 

The efficiency of the Sila-Stetter reaction for the synthesis of 1,4-dicarbonyl compounds prompted us to extend this methodology to a single-flask protocol for the Paal-Knorr synthesis of furans and pyrroles [82, 83]. Finally, we also took advantage of acylsilanes to develop the 1,2-addition of carbanion equivalents to activated imines for the synthesis of a-amino ketones [84]. 

The benzoin condensation is the coupling of two aldehyde molecules to give an a-hydroxyketone (acyloin) product. In its most classical form, the homocoupling of benzaldehyde gives the parent benzoin (R = R = Ph). Contemporary modifications of the benzoin condensation include the use of acylsilanes as well as imine derivatives in place of one aldehyde partner. ... 

When lithium enolates derived from amides react with acylsilanes, the resulting /ff-lithioamides or homoenolates are stabilized by intramolecular coordination of a amide carbonyl group and react with electrophiles such as allyl bromide and imines to give y hydroxy yff-substituted amides (Scheme 3-153). 

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