Dialkoxysilanes

Tamao and Ito have reported a nickel-catalyzed protocol for the cyclization/hydrosilylation of 1,7-diynes to form (Z)-silylated dialkylidene cyclohexane derivatives.For example, reaction of 1,7-octadiyne with triethoxysilane catalyzed by a mixture of Ni(acac)2 (lmol%) and DIBAL-H (2mol%) in benzene at 50°G for 6h gave the corresponding silylated dialkylidene cyclohexane in 70% yield as a single isomer (Table 1). The reaction of 1,7-octadiyne was also realized with mono- and dialkoxysilanes, trialkylsilanes, and dialkylaminosilanes (Table 1). Diynes that possessed an internal alkyne also underwent nickel-catalyzed reaction, albeit with diminished efficiency (Table 1), while 1,6- and 1,8-diynes failed to undergo nickel-catalyzed cyclization/hydrosilylation. 

Similar experiments using silane concentration as the variable showed that the highest IFSS values were observed for application from 0.5 wt% concentration for all three silanes studied. The typical results shown in Table 3 for the polymeric dialkoxysilane illustrate this trend. It can be seen that the IFSS of the specimens under dry conditions is highest when the silane concentration is 0.5 wt% in the application solution. Furthermore, it should be noted that after 1 h boiling in water, retention of IFSS is also highest for this set. 

Dependence of the interfacial shear strength (IFSS) in SFC specimens on the polymeric dialkoxysilane PS076.5 concentration in aqueous solution"... 

An alternative route to l-organyl-2-carbasilatranes involves the reaction of organyl(3-chloropropyl)dialkoxysilanes with diethanolamine393-396. For example, phenyl(3-chloropropyl)dimethoxysilane is converted to 155 (38%) by treatment with diethanolamine in xylene (equation 163). Triethylamine acts as an HC1 acceptor394. 

An effective cross-coupling of alkynes using silicon-tethered Fe(CO)s-promoted cyclocarbonylation was shown to provide a seven-membered ring dialkoxysilane 302, which subsequently upon treatment with Me3NO in acetone at 0°C was converted to cyclopentadienones 303 with variable substituents (Scheme 54) <2002OL2837>. 

Anhydrous trimethylamine N-oxide has been suggested as an alternative, neutral oxidant, although with dialkoxysilanes relatively high reaction temperatures are required. Alkyltrifluorosilanes, on the other hand, undergo cleavage with this oxidant at room temperature. ... 

Several control experiments showed that dichloro- and dialkoxysilanes would react with... 

The nature of the leaving groups is also critical the ratio = 0.56 x k " suggests that dichlorosilanes are about two times more reactive than dialkoxysilanes and this is supposedly the reason why, other conditions being equal, the process with alkoxysilanes is visibly more selective [7]. 

In agreement with the competitive kinetic measurements, dichlorosilanes react faster than dialkoxysilanes. Bulkier substituents slow the process compared to less encumbering substituents at Si (Table 2). For triethylsilane, used as silanone trap, it was found that Si-H bond is also reactive... 

For a better understanding of the probe behavior in PDMS networks it was necessary to investigate the fluorescence behavior of a probe covalently bonded to a soluble polydimethylsiloxane chain. Therefore, a dialkoxysilane containing 4-piperidinobenzoic acid ester was allowed to react with a hydroxyl-terminated polydimethylsiloxane giving a soluble polymer with a covalently bonded probe at the main chain. This reaction occurs in the presence of Sn(II) octoate. The reaction scheme is drawn in Fig. 4. It was shown by GPC (UV detection) and NMR spectroscopy that the probe reacted with the hydroxyl groups of the polydimethylsiloxane chains. 

Cohen, Y., Kotlyar, V., Koeller, S., Lellouche, J.-P. Reaction of C2-symmetrical dialkoxysilanes R 0-Si(R )2-OR with the two Viismeier-Haack complexes POCI3.DMF and (CF3S02)20.DMF an efficient one-step conversion to the corresponding formates R1-OCHO. Synlett 2001, 1543-1546. 

Reactions of Chiral Prochiral Dialkoxysilanes with Ethyllithium (86)... 

The first example of an asymmetric induction at tetragonal silicon was reported by Klebe and Finkbeiner42 and is shown in equation 3. The reaction of a prochiral bis-(acetamido)silane with optically active amino acids led to two diastereomeric 2-silaoxa-zolidones in unequal amounts. These diastereomers were shown to undergo a second-order asymmetric transformation crystallization was accompanied by a rearrangement of the less abundant into the more abundant diastereomer. From the silaoxazolidones, alcoholysis reactions yielded an optically active dialkoxysilane. 

TABLE 7. Reactions of chiral prochiral dialkoxysilanes with ethyllithium (after Reference 55)... 

Another very useful route to vinylsilanes is hydrosilylation of alkynes by means of chlorosilanes, trialkoxysilanes, methyldichloro- or dialkoxysilanes, respectively, as catalyzed by ruthenium-, rhodium- or platinum complexes (equation 43a)62. A well-known example is the reaction of 31 with 7 in the presence of a ruthenium complex (equation 43b)62. 

Tethering through dialkoxysilanes. The linking of hydroxyl groups from two molecules favor their subsequent reaction. More important, the tactic affords stereo-control in these reactions, as shown in an intramolecularized glycosylation. 

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