Silyl amino-substituted

Nucleophilic substitution with lithium hexamethyldisilazane (LiHMDS) proceeds with inversion to give silylated amino boronic ester 19.26 A solution of 19 is passed through a short plug of silica before its use in the desilylation reaction. Due to the instability of underivatized a-amino boronic esters,26 trifluoroacetic acid (TFA) is used to furnish the corresponding TFA salt 20.27 A second recrystallization from TFA and isopropylether further enhances the optical purity. A diastereomeric ratio (dr) > 97 3 is typically obtained from the process route. 

Silylated amino acid esters have been prepared by a dynamic kinetic asymmetric transformation of this type. Slow addition (by syringe pump) of (R,R) DPEC maintained insertion slow relative to interconversion and afforded the silyl-substituted amino acid esters in Eq. 36 with ee values of 80, 68, and 83%. The ester 38c (R=TMS) was too base-sensitive to permit removal of the chiral diol, but transesterification of the other /J-hydroxyethyl esters 38 to the corresponding methyl esters was straightforward [22]. 

The highly reactive silyl ttiflates and silyl bis(triflates) are obtained by reaction of the corresponding aminosilanes with triflic acid in diethylether as shown in Schemes 1 and 2 [12]. The substitution patterns at the silicon atoms are variable. Functional substituted silanes, e.g., vinyl, allyl, or hydrogen derivatives can also be obtained. (Diethylamino)diphenylsilyllithium is formed from (diethylamino)diphenylchlorosilane with lithium in THF. Yields of both reactions are high (90-95%). The products can be used for following reaction without further purification. Silyl triflates and (aminosilyl)lithium compounds react to give the amino-substituted trisilanes la - Ic (Scheme 1). 

Among the more reactive and synthetically useful dienes are doubly and triply activated alkoxy- and amino-substituted dienes, such as ( )-l-methoxy-3-(trimethylsilyloxy)-1,3-butadiene (Danishefsky s diene),( )-l-(dimethylamino)-3-(fert-butyldimethylsilyloxy)-1,3-butadiene (Rawal s diene)-, and 1,3-dimethoxy-l-(trimethylsilyloxy)-1,3-butadiene (Brassard s diene). As illustrated below, the cyclo-addition products arising from these dienes can either be hydrolyzed or treated with fluoride ion to remove the silyl group, which is followed by (3-elimination to provide conjugated cyclohexenones. 

Another route to amino substitution is the exchange of alkoxy or siloxy groups, which arc accessible by Oalkylation, e.g. by a Mitsunobu reaction with methanol,331 or O-silylation of hydroxy or oxo functions.83 Thus, piperazine reacts with 2-alkoxy-8-ethyl-5-oxo-5,8-dihy-dropyrido[2,3-rf]pyrimidine-6-carboxylic acids, e.g. 8,335,336 or with 8-ethyl-2,5-dioxo-l,2,5,8-tetrahydropyrido[2,3-c/]pyrimidine-6-carboxylic acid (9), after silylation by hexamcthyldisila-zane.337 338... 

Chlorine atoms in the 1-position of thiatriazines are readily attacked by secondary amines. Amines with high nucleophilicity and, generally, primary amines cleave the thiatriazine ring system at the endocyclic S - - N bond. Only one case is known in which an excess of secondary amine leads to 1,3-disubstituted thiatriazinamines.28 Even silylated amines react in the first reaction step in the 1-position. 5-Chloro-A,./V-dialkylthiatriazine-l,3-diamines do not react with amines or silylated amines. Compounds of type 2 react selectively with amines to give 1-amino-substituted thiatriazines 3.30,31,47... 

The exchange of chlorine for a dialkylamino unit in sulfur-containing heterocycles is a well-established procedure.14 The reaction of silyl-substituted amines with C-CI, P-Cl, and S—Cl bonds at low temperature in an aprotic solvent or without solvent yields the corresponding amino-substituted compounds, e.g. formation of 2.25... 

Amino-substituted silylanions were introduced by Tamao and have proved to be valuable synthetic building blocks. In our case, the objective to prepare aminooligosilylanions was driven by the intention to incorporate a site suitable for further functionalization, as well as by the prospect of obtaining transition metal silyl ligands with additional coordination sites. 

Summary Amination of chlorosilanes with dialkylamine allows the synthesis of various chloro- and amino-substituted oligosilanes. The remaining reactive chloro sites enable to bond further hinctionalities as well as other silyl units to the silane. In this procedure the amino group is protecting potentially reactive sites at silicon atoms and can be easily exchanged by chloro substituents. By this route a desired silicon architecture can be built up. 

In order to introduce groups into the silyl anion, which can be used for further functionalization, we also investigated reactions of hydride and amino-substituted bis(trimethylsilyl)silylpotassium compounds with the metallocenes. Both types of compounds underwent the transformation smoothly (Scheme 1). 

It is interesting to note that condensation of the N,N-bis(silylated) enamine 538 with a variety of chalcones such as benzalacetophenone 735 proceeds, via 539 and subsequent cyclization and oxidation, to pyridines such as 540 [106, 108] whereas persilylated co-amino ketones such as the 2-substituted pyridine 541 cyclize, via 542, in 29% yield, to the pyrrole 543 [109] (Scheme 5.36). 

For example, substituents in terminal olefins (43) in the resulting nitronates (35) are generally adjacent to the C-6 atom. The alkoxy and siloxy substituents from vinyl ethers and silyl enolates respectively, as well as the amino group from enamines, are oriented in the same positions. In the case of tris-substituted olefins, C-6 is the most crowded atom in the resulting nitronates. 

Mamyama et al.25 have obtained high-molecular-weight poly(benzoxazole)s by the low-temperature solution polycondensation of A,A 0,0 -tetrais(trimethyl-silyl)-substituted 2,2-bis(3-amino-4-hydroxyphenyl)-l,l,l,3,3,3-hexafluoro-propane (25) with aromatic diacids and subsequent thermal cyclodehydration of the resulting poly(o-hydroxy amide)s in vacuo. In this method, aromatic diamines with low nucleophilicity are activated more positively through the conversion to the /V-silylated diamines, and the nucleophilicity of the fluorine-containing bis(o-aminophenol) can be improved by silylation. 

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