Alkoxy groups, terminal, synthesis

The reaction was extended to 1,3-dienyltins, giving the corresponding lithiated reagents, both in terminal or internal position, which can be substituted by alkoxy groups . Recently, a 1,3,5-trienyl lithium carbanion was prepared in a similar way from 22 and used for a further synthesis (equation 48) . 

In the next step of the dendrimer synthesis, treatment of the dichloromethylsilyl-capped product with allylmagnesium bromide provides eight terminal alkenes and provides the first-generation product. Subsequent cycles of hydrosilylation and alkylation provide the second- and third-generation dendrimers in similar fashion. The third-generation dendrimers were ultimately capped with phenols, pendant allyl- or alkoxy- groups, or phenylethylene units. ... 

Many of the earlier schemes in this section show examples of the synthesis of alkyl, alkoxy and cyano terminal groups alkyl and alkoxy groups are also conveniently generated in alternative ways from halides and phenols as shown in Scheme 8. If the alky-nyl coupling shown in Scheme 8 for 8.1 is carried out with the phenolic triflate 8.2, then subsequent reduction of the product to the alkyl group gives a way of creating an alkyl unit at a phenolic site. 

The poly(siloxane) polymers are usually prepared by the acid or base hydrolysis of appropriately substituted dichlorosilanes or dialkoxysilanes, or by the catalytic polymerization of small ring cyclic siloxanes [71-75]. The silanol-terminated polymers are suitable for use after fractionation or are thermally treated to increase molecular weight and in some cases endcapped by trimethylsilyl, alkoxy or acetyl groups [76,77]. Poly(siloxanes) synthesized in this way are limited to polymers that contain substituent groups that are able to survive the relatively harsh hydrolysis conditions, such as alkyl, phenyl, 3,3,3-trifluoropropyl groups. Hydrosilylation provides an alternative route to the synthesis of poly(siloxanes) with labile or complicated substituents (e.g. cyclodextrin, oligoethylene oxide, liquid crystal, amino acid ester, and alcohol) [78-81]. In this case... 

The structure of the products is determined by the site of protonation of the radical anion intermediate formed after the first electron-transfer step. In general, electron-releasing substituents favor protonation at the ortho position, whereas electron-attracting groups favor protonation at the para position. Addition of a second electron gives a pentadienyl anion, which is protonated at the center carbon. As a result, 2,5-dihydro products are formed with alkyl or alkoxy substituents and 1,4-reduction products are formed with carboxylate substituents. It has been suggested that the reason the pentadienyl anion is protonated at the center carbon is that this causes a smaller change in bond orders than protonation at one of the terminal positions. " The reduction of methoxybenzenes is of importance in the synthesis of cyclohexenones via hydrolysis of the intermediate enol ethers ... 

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