Grignard complications

The Nef reaction is accelerated by the presence of silicon atom at y-position of nitro functions, as shown in Eq. 6.3. The presence of the y-silicon is essential for such smooth reaction.6 The conversion of 5-nitrobicyclo[2.2.1]heptenes to the corresponding ketones via the Nef reaction is very complicated by the degradation of the product. Thus, (3-trimethylsilyl ketones can be prepared by a one-flask method via the addition of Grignard reagents containing trimethylsilyl groups to nitroalkenes and the subsequent hydrolysis, as shown in Eq. 6.4. 

In Grignard reactions involving GeCl4, complications usually arise because of the possible generation of intermediates like XR2GeMgX. Such intermediates can explain the formation of cyclotetragermanes20. 

In 1974, Vermeer et al. described formation of allenic alcohols 61 by the reaction of alkynyl epoxides 60 with Grignard reagents in the presence of 10mol% of Cul (Scheme 3.33) [71]. In the absence of Cul, a complicated mixture of products was obtained. Furthermore, the Cu-catalyzed reactions exhibited higher yields and higher selectivity than analogous reactions of alkynyl epoxides with lithium dialkylcup-rates [72], This method was applied to a reaction of allylmagnesium bromide with an alkynyl epoxide [73]. 

Only formaldehyde yields a primary alcohol by reaction with a Grignard reagent. Figure 14-3 illustrates the reaction of ethylmagnesium bromide with formaldehyde to form 1-propanol. More-complicated alcohols, such as cyclopentylmethanol, can be synthesized by this means (as shown in Figure 144). 

Acylation of the heteroaryl Grignard compounds generally yields the C-acyl derivatives, but the reaction tends to be more complicated than the alkylation reactions. It is noticeable that the Grignard compounds react with the harder carbonyl compounds with the formation... 

---