Orthoesters reaction with Grignard reagents

The reaction of orthoesters with Grignard reagents provides a well known route to acetals and ketals U->-2). Eliel and Nader (1) have investigated the stereochemistry of this reaction and have concluded that it is governed by powerful stereoelectronic effects. 

Scheme 2.17. Reactions of cyclic orthoesters with Grignard reagents [57].

It is not necessary that such alkylalkoxysilanes be formed in this manner alone, however, for they can be prepared from the orthosilicates by direct reaction with zinc alkyls55 or with the Grignard reagent, as was pointed out in the section on the orthoesters. It follows that there may be mono-, di-, and trialkyl derivatives of ethyl silicate just as mono-, di-, and trialkyIchlorosilanes are obtained from silicon tetrachloride. The same is true of every other silicon orthoester, so that many different organosilicon compounds are possible even within... 

In agreement with the results obtained with the titanium alkoxide, titanium tetrachloride converts the 6-substituted alkene orthoester 49 into the expected cyclohexanone 48 in 88% yield, and Grignard reagents promote the carbocy-clization reaction and then react with the carbonyl functions of the products. In this way compound 49, on treatment with phenylmagnesium bromide, affords the diphenyl product 50 that has both of the phenyl groups equatorial (Scheme 11) [46]. 

---