4- Amino-3-silyl

As shown in Scheme 9.10, the silylene 3 underwent oxidative additions with alkali metal (M) bis(trimethylsilyl)amides to give new alkali metal amides, rather than metal fais(amino)silyls M[SifN. ) N(SL Ie3)2 ](thf), which, however, were suggested to have been intermediates.Whereas M[N Si(NN)fSi. Vie ,) (Si. Vlc ) (thfwith R = Me underwent a further reaction with 3 to yield M[N Si(NN)(SiMe3) 2], for R = Ph the double addition compound was the sole product in the 3/Li[N(SiMe3)(SiMe2R)] system. ... 

Aldol condensation of a-amino silyl ketene acetals (l).10 2-Dibenzylami-noketene trimethylsilyl acetals (1) react with aldehydes premixed with TiCl4 to give a-amino-p-hydroxy carboxylic esters (2) with moderate to high syn-selectivity. Surprisingly, TiCl4-catalyzed reaction of 1 with a chiral a-alkoxy aldehyde proceeds with low asymmetric induction. 

Methylhydroxycarbene, MeC(OH), has been generated in one of the three reaction pathways of the collision-induced dissociation of protonated butane-2,3-dione.13 Its enthalpy of formation was found to be 16 4 kcalmol-1. Fluorophenoxycarbene (PhOCF) has been generated inside a hydrophobic hemicarcerand (1) by irradiation of the corresponding confined diazirine.14 Its reactivity (especially dimerization and reaction with water) was significantly lowered by the incarceration, allowing its persistence for days at room temperature. New (amino)(silyl)carbenes (2) have been generated and their structure-activity relationship studied. They showed behaviour similar to those of previously reported (amino)(alkyl)carbene.15... 

R = alkyl, aryl, alkenyl, alkynyl, amino, silyl Figure... 

The structures of three heteroleptic digermenes, 69-71, have been reported. In 69 each Ge bears a terphenyl group and a Cl atom in 70 and 71 ° tris(amino)silyl and amino substituents are present at each Ge. While 69 and 70 are fi-isomers, 71 adopts the unusual Z-form. The electronegative chloro or amino groups cause large trans-b at angles between 39° and 47.3° and long Ge=Ge bonds between 244.3 and 246.0 pm. 

Possible precursors for silyleneboranes might be amino(silyl)boranes with stericaUy bulky amino and silyl groups. For this reason silylboranes of types R Si-B(tmp)X and tmpB-... 

Schraml et al.(137) found that the Si resonances of a series of silyl ester, alkoxy-silyl, and amino-silyl derivatives appear in different regions of the spectrum. On the basis of this information they suggested that Si NMR can be used for the structure elucidation of silylated hydroxy- or aminoacids. The silicon chemical shifts for DL-serine [55] and DL-threonine [56 ] are shown in ppm. The variation in the shielding for the alkoxy-silyl group demonstrates the previously noted sensitivity of Si NMR to the nature of R in Mc3SiOR. (140)... 

Both compounds 5 and 8 readily react with primary amines giving the corresponding tris(amino-silyl)methanes and -silanes (Scheme 2). 

C.G. Golander and E. Kiss, Quantitative measurements of amino silylation on plasma-activated mica surface. Colloids and Surfaces, 74, 217-222(1993). 

Similarly, various amino-alkyl and amino-silyl, carbenes have been prepared and studied. 

Conjugate Addition. Conjugate addition of trimethylsilyl diethylamine to enones gives /3-amino silyl enol ethers. Thus, in the presence of catalytic amounts of trimethylsilyl triflate, trimethylsilyldiethylamine adds to ethyl vinyl ketone in a 1,4-fashion. The reaction requires 50 mol % excess of trimethylsilyldiethylamine, and proceeds in ether at room temperature under nitrogen. The product Af,A -diethyl-3-[(tiimethylsilyl)oxy]-( )-2-pentamine is distilled out under reduced pressure in 45% yield (eq 18). The major product is the -enol ether containing approximately 5% of other trimethylsilyl ether isomers. 

Early attempts to produce cephalosporin analogs by varying the 7-acylamino substituent were frustrated because, in contrast to previous experience with penicillins, a good method for producing the necessary 7-amino compound (33a) could not be found. This problem was finally solved when it was discovered that diazotization of the a-aminoadipyl residue produces an iminolactone (33b) which can be hydrolyzed to the free amine in good yield. Subsequently an improved procedure was developed which involves silylation of the carboxyl groups followed by reaction with phosphorus pentachloride to yield iminochloride (33c)... 

Me3SiNEt2- Trimethylsilyldiethylamine selectively silylates equatorial hydroxyl groups in quantitative yield (4-10 h, 25°). The report indicated no reaction at axial hydroxyl groups. In the prostaglandin series the order of reactivity of trimethylsilyldiethylamine is Cii > Ci5 C9 (no reaction). These trimethylsilyl ethers are readily hydrolyzed in aqueous methanol containing a trace of acetic acid. The reagent is also useful for the silylation of amino-acids. ... 

A-Methyl-N-trimethylsilylacetamide. This reagent has been used prepa-ratively to silylate amino acids. 

Alkyldithio carbamates are prepared from the acid chloride (Et N, EtOAc, 0°) and amino acid, either free or as the O-silyl derivatives (70-88% yield). The N- i-propyldithio) carbamate has been used in the protection of proline during peptide synthesis. Alkyldithio carbamates can be cleaved with thiols, NaOH, Ph P/TsOH. They are stable to acid. Cleavage rates are a function of the size of the alkyl group as illustrated in the table below. 

These conditions were chosen specifically to facilitate the silylation of hydroxylated amino acids. 

The assumed transition state for this reaction is shown in Scheme 5.5. The two bulky t-butoxy groups are expected to locate at the two apical positions. One of the 3,3 -phenyl groups would effectively shield one face of an imine, and consequently, a diene attacks from the opposite side. Judging from this model, similar selectivities were expected in the Mannich-type reactions of imines with silyl eno-lates. Actually, when ligand 10 was used in the reaction of imine la with S-ethyl-thio-l-trimethylsiloxyethene, the corresponding / -amino thioester was obtained in 84% ee (Scheme 5.6). As expected, the sense of the chiral induction in this case was the reverse of that observed when using catalyst 6 [12, 25]. 

Several approaches based on nitro-aldol for the synthesis of amino sugars have been reported Alumina-catalyzed reaction of methyl 3- nitropropanoate with O-benzyl-o-lactaldehyde gives the o-ribo-nitro-aldol fanti, and isomeri in 63% yield, which is converted into L-dannosamine fsee Secdon 3 3 Jager and coworkers have reported a short synthesis of L-acosamine based on the stereoselective nitro-aldol reaction of 2-O-benzyl-L-lactaldehyde with 3-nitropropanal dimethyl acetal as shovm in Scheme 3 10 The stereoselecdve nitro-aldol reacdon is carried ont by the silyl nitronate approach as discussed in Secdon 3 3... 

Aldol additions of various lithium enolates performed in the presence of (S.S)-l, 4-bisdimethyl-amino-2,3-dimethoxypentane or (.SVS )-1,2,3,4-tctramethoxybutane display only modest reagent-induced stereoselectivity (<20% ee)21. Significant improvement results from the use of the proline derived diamines 2,3 and 4 as additives in tin(II) mediated aldol additions of silyl enol ethers22 23. 

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