Silyl imines

In a similar type of process, imines have been dimerized to give 1,2-diamines, by a number of procedures, including treatment with TiCLj—In/aqueous EtOH, Zn/aqueous NaOH, Cp2VCl2/Zn/PhMe2SiCl, with Sml2, and I for silylated imines) NbCl4(thf)2. When electroreduction was used, it was even... 

N-silylated imines 509 react with the Li salts of tosylmethylisonitriles to give 4,5-disubstituted imidazoles in moderate yields [93]. Acetylation of N-trimethylsilyl imines 509 with acetyl chloride and triethylamine affords 72-80% of the aza-dienes 510 these undergo readily Diels-Alder reactions, e.g. with maleic anhydride at 24 °C to give 511 [94] or with dimethyl acetylenedicarboxylate to give dimethyl pyridine-3,4-dicarboxylates [94] (Scheme 5.29). 

Boron aldol reactions have been used to stereoselectively construct the anti-3-hydroxy-2-methylcarbonyl system from carboxylate esters,58 and to combine a-hetero-substituted thioacetates with aldehydes or silyl imines enantio- and/or diastereo-selectively.59... 

Other precursors like 741 and 742 were pyrolysed under similar conditions, but here the energetically favoured, competitive retro-ene process leading to the silyl imines 743 was predominant (equation 244). 

These silyl imines are generated in situ from the corresponding aldehydes resulting in a reduction of the number of reaction steps and simplifies the work-up procedures (figure 8). Another option is to convert the aldehyde into a N-tosyl or a N,N-dimethylsulfamoyl irnine23. 

A new protocol for the stereoselective synthesis of (i-lactams [213] has been reported to be performed by a conrotatory ring closure of l-halo-3-aza-4-alkyl-l, 3-dienes, previously prepared by Staudinger methodology, (for the synthesis and chemistry of /V-silyl imines see [214] for [2+2] cycloaddition of /V-silyl imines and ketenes see [215]) in refluxing toluene (Scheme 96). 

Scheme 4 Stepwise mechanism corresponding to the reaction between ketenes and IV-silyl imines...

As we have indicated previously, the reaction between ketenes and (V-silyl imines was described by Pannunzio et al. [30-33] and constitutes an interesting version of the Staudinger reaction between ketenes and imines because of the isolation of the intermediate of silyloxyazadienes. Given its interest, this reaction has been studied by different groups [92-94],... 

Acrylonitrile and methacrylonitrile (MAN) polymerize extremely rapidly by GTP [9]. Molecular weight control is difficult since the polymers form before uniform mixing occurs. Although 7a can be used to initiate MAN, MTS is better. The silyl imine end 7b is the likely chain carrier (Scheme 7). 

German, C. Vulpetti, A. Pain, G. Highly enantio- and diastereoselective boron aldol reactions of a-heterosubstituted fhioacetates with aldehydes and silyl imines. Tetrahedron 1997, 53, 5909-5924. 

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. 

Insertion of isonitriles and carbenoids into the B-B and B-Si bonds have recently been developed as a method for synthesizing geminal bis(boryl) and boryl-silyl compounds (Scheme 24). The insertion of alkyl and aryl isonitriles into the B-Si bond proceeded at room temperature to provide monomeric (boryl)(silyl)imines 227.388,389 Alkylidene... 

Recently, it was described that the addition of the 5,5-bis(hydroxymethyl)-l,3-dithiane to an in situ generated IV-silylated imine provided the corresponding amine, used for the preparation of photolabile phospholipids358. 

Diazadienes 370 and 371, formed in situ from the corresponding silyl imine and phenylisocyanate, readily undergo [4 + 2] cycloadditions with enamines derived from butyraldehyde and cyclohexanone leading, after deamination, to pyrimidone 372 and pyrimidothione 373, respectively224. 

Insertion of isonitriles into Si-Si bonds takes place in the presence of palladium catalysts to give bis(silyl)imines 85, which show characteristic UV absorbance around 400 nm arising from n-Ji transition (Eq.43) [79]. Aryl and alkyl isonitriles except for tertiary alkyl isonitrile give the corresponding N-substituted imines. 

Boranes other than those based on a-pinene are particularly useful in allylic transfer to imines to make single enantiomers of unsaturated amines. One good combination is an allylboron compound 80 complexed with an /V-sulfonyl amino alcohol such as 78, derived from nor-ephedrine (see chapter 23) with an /V-silyl imine such as 81. The unsaturated amines 82 are formed in good... 

For a reverse electron-demand Diels-Alder with azadienes, Barluenga8 reacted stable silylated imines 65 of unenolisable aldehydes (R = Ar or cinnamyl) with acetylene dicarboxylic esters to give the 2-azadienes 67. 

The tremendous success in the catalytic asymmetric addition of organozinc reagents to aldehydes spurred Itsuno and co-workers to examine the reactivity of diethylzinc with silyl imines in the presence of chiral amino alcohols and diols. Unfortunately, this type of azomethine function failed to react [23a]. The use of activated N-acyl- and iV-phosphinoylimines turned out to be crucial as evidenced by the following reports on the alkylation of these functions using di-... 

Acetonitrile ylide was generated from a-silyl imine 63 and silver fluoride. This same ylide could be generated from the reaction of methylene with acetonitrile. The chemo-selective silicon- fluoride ion route seems best, however, offering the advantages of readily available, easily handled reagents. The so-generated ylide was cycloadded to several... 

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