Epoxide chlorosilanes

Epoxides are versatile intermediates in organic synthesis owing to the possibility of controlled stereoselective ring opening. The ability of various chlorosilanes to serve as a source of chloride ion for the opening of epoxides was first recognized... 

Deoxygenation via iodohydrin intermediates using chlorosilane/sodium iodideand p-toluenesul-fonic acid/sodium iodidehas also been reported. In a natural product synthesis, an epoxide has been deoxygenated with a large excess of triethylsilane at 300 C for 30 h (equation 51). 

Using route II [1], the desired silanes are accessible in a two-step synthesis The ft)-epoxyalkenes are obtained by partial epoxidation of the corresponding a,dienes with w-chloroperbenzoic acid. The lower product yields (47-50 %) compared to the direct epoxidation of side-reaction. The subsequent hydrosilylation requires the ethoxysilane HSi(OEt)3 as educt in order to exclude ring opening during the otherwise nescessary alcoholysis step. The lower reactivity of HSi(OEt)3 compared to chlorosilanes significantly reduces the formation of isomers but, on the other hand, considerably decreases the product yields (31-70 %). 

BENZYL FORMATE (104-57-4) C,H,Oj Forms explosive mixture with air (flashpoint 107°F/42°C). Violent reaction with oxidizers. Incompatible with nitrates bases, amines, amides, inorganic hydroxides boranes, chlorosilanes epoxides hydroxy compounds. On small fires, use dry chemical powder (such as Puiple-K-Powder), foam, or COj extinguishers. 

In Fig. 10, reaction of 1 with chlorosilane 6 yielded the N-silyl derivative 7 that was not isolated but directly transformed into alkene 8 (the precursor of epoxide 3 of Fig. 9) under Sakurai s conditions. Both the yield (50%) and the stereoselectivity (80 20 for the indicated isomer) were not very high, but the road was paved toward a better process. 

Over the last decade, a considerable number of reactions has been studied (11,35) (i) olefins oxidation (38,39), hydroboration, and halogenation (40) (ii) amines silylation (41,42), amidation (43), and imine formation (44) (iii) hydroxyl groups reaction with anhydrides (45), isocyanates (46), epichloro-hydrin and chlorosilanes (47) (iv) carboxylic acids formation of acid chlorides (48), mixed anhydrides (49) and activated esters (50) (v) carboxylic esters reduction and hydrolysis (51) (vi) aldehydes imine formation (52) (vii) epoxides reactions with amines (55), glycols (54) and carboxyl-terminated polymers (55). A list of all the major classes of reactions on SAMs plus relevant examples are discussed comprehensively elsewhere (//). The following sections will provide a more detailed look at reactions with some of the common functional SAMs, i.e hydroxyl and carboxyl terminated SAMs. 

An alternative entry into the system has been developed in which an a-chloro-methylvinylsilane (843) is epoxidized and the product subjected to a fluoride-promoted chlorosilane elimination, the resulting cyclopropanone being trapped with dienes. This promises to be a valuable new route to seven-membered rings and to bicyclo-[3,2,1] structures. ... 

Thus in the aldol addition, just as in the case of epoxide-opening reactions, the chloride ion, formed as a necessary consequence of the mechanism of Lewis base catalysis with chlorosilanes, is not innocuous. In fact, it is a competent nucleophile that can attack an aldehyde or an epoxide activated by the Lewis base-coordinated silicenium cation in an intermolecular fashion. The desire to understand these two seemingly inconsistent results obtained in our study of the Lewis base-catalyzed reactions of trichlorosilanes presented an opportunity for the development of novel catalytic processes. For example, if a chloride ion can capture these activated electrophiles, could other exogenous nucleophiles be employed to intercept these reactive intermediates If so, a wide variety of bond-forming processes mediated by the phosphoramide-bound chiral Lewis acid [LB SiCls]" would be feasible. At this point it remained unclear if (1) an exogenous nucleophile could compete with the ion-paired chloride and (2) what kinds of nucleophiles could be compatible with the reaction conditions. 

Denmark SE, Barsanti PA, Wong K-T, Stavenger RA (1998) Enantioselective ring opening of epoxides with chlorosilanes in the presence of Lewis-bases. J Org Chem 63 2428-2429... 

According to this mechanism (Scheme 15.29), the process is amendable to asymmetric modifications. Among various silicon reagents that were examined, only tetrachlorosilane proved to be suitable for the asymmetric process, while application of other chlorosilanes resulted in the formation of racemic products. Several chiral Lewis bases were investigated in the opening of meso-epoxides 146 and 151 (Scheme 15.30) to produce the corresponding chlorohydrins 150 and 152, respectively. Opening of the norbornene-derived epoxide 153 was found to proceed... 

Ester, anhydride, nitrile, chlorosilane and epoxide are the electrophilic functions most commonly used for grafting onto reactions with strongly nucleophilic carbanions. 

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