Dialkoxy silane

The compounds I and II represent intermediates for the synthesis of either carboxy functional or amino functional polysiloxanes. To this end I or II is either saponified with sodium hydroxide and concomitantly polycon-densated to a poly(carboxylaIky1 methyl siloxane) (III) or reduced to an amino alkyl methyl dialkoxy silane with sodium borohydride (J 5). ... 

Figure 1. (a) Polymeric aminofunctional silane-carrying dialkoxy silane groups, (b) Multiple sawhorse -type siloxane bonding to the fiber surface. 

Scheme 1. Autocyclization and oligomerization of silanones electrogenerated from dichloro- and dialkoxy silanes.

Another noteworthy feature of the polymeric silane depicted in Fig. la is that the silane chains on the polymer backbone carry dialkoxy groups. In comparison with monomeric silanes which carry trialkoxy groups, these polymeric silanes are claimed to offer superior substrate reactivity and to provide further performance improvements [4, 5]. A probable explanation seems to be the difference in the number of siloxane bonds that can possibly be formed with the glass surface by the two types. 

Reductive cleavage of the carbon-silicon bond of acyl silanes, including a-alkoxy and t/./i-dialkoxy derivatives, to give aldehydes may be accomplished by palladium-catalysed hydrogenolysis at ambient temperature and pressure212. 

Table 13 Ratio of Diastereoisomers in the Reactions of Nonstereogenic Enol Silanes with Chiral a,p-Dialkoxy...

An interesting approach to chiral 2-amino-1,3-diols makes use of an asymmetric Staudinger reaction that incorporates the required functional groups into a jS-lactam nucleus. The condensation of imine 818 with benzyloxyketene produces jS-lactam 819 with 95% diastereo-selectivity [218]. After dearylation with cerric ammonium nitrate the amino polyol is released as an isoserine derivative (821) by cleavage of the jS-lactam with chlorotrimethylsilane in methanol [227] (Scheme 110). The amino group can be removed by conversion to isocyanide 823 followed by reduction with tris(trimethylsilyl)silane in the presence of AIBN, which furnishes erythro a,j8-dialkoxy ester 824 without racemization. 

A further valuable tool in organic chemistry is facilitated by isocyanides the deamination reaction. When the standard deamination reaction via a diazonium salt is undesirable (due to a need to avoid acidic conditions), primary amines can be converted by well-known methods into isocyanides, which are reduced using tri-butyltin hydride under Bartorf s conditions (heating for 5 h at 80 °C in toluene). This reaction sequence has been applied as a new route to 1,3-polyols using azetidinone frameworks 1565 as chiral templates [1188]. Dehydration of the formamide 1567 was accomplished with triphosgene to afford the isocyanide 1568, which was reduced efficiently with tris(trimethylsilyl)silane to afford the desired a,y-dialkoxy ester 1569 in 80% yield [1188]. 

Koe JR, Powell DR, Buffy JJ, West R (2000) Octachlorocyclotetrasilane, perchloropoly silane and new dialkoxy- and diaminopolysilanes. In Auner N, Weis J (eds) Organosilicon chemistry IV from molecules to materials. Wiley-VCH, Weinheim... 

Nucleophilic additions to a,3-dialkoxy aldehydes via allyl silanes (eq 3) or silyl ketene acetals (Mukaiyama reaction) (eq 4) exhibit similarly high selectivities. a-Thio aldehydes also react under MgBr2-catalyzed Mukaiyama conditions with efficient stereocontrol (eq 5). ... 

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