Ketones and Grignard reagents

Three combinations of Grignard reagent and ketone give rise to tertiary alcohols... 

The introduction of alkyl groups into steroids is generally achieved by means of the following types of reactions between Grignard reagents and ketones or epoxides. 

Table 45 Secondary j8-deuterium KIEs in the free radical reactions between Grignard reagents and ketones at 25°C.a...

Note that aii three procedures require a Grignard reagent and a ketone. Note also that procedures 1 and 3 require the same Grignard reagent and ketone. Thus, our choice comes down to whether to use procedure 1 or procedure 2. If we use procedure I, we can start with the needed ketone since it contains only four carbons. If we use procedure 2, we cannot start with the required ketone because it contains five carbons. Let us, therefore, use procedure I because it will require fewer steps. 

How can C be broken up so that the structures of the required Grignard reagent and ketone may be deduced Answer Since C is a tertiary alcohol, there are three carbon-carbinol carbon bonds which may be cleaved to reveal the needed starting materials. 

Acetylenic tertiary alcohols are prepared from sodium acetylides or acetylenic Grignard reagents and ketones in the same manner as described for primary and secondary alcohols (method 88). Dimethylethynylcarbinol is prepared from acetone, aqueous potassium hydroxide, and acetylene in an autoclave at 100° and 300 p.s.i. Ketones ate sometimes treated with an acetylide prepared from acetylene and a solution of sodium or potassium alkoxide in /-amyl alcohol. " Another procedure utilizes... 

In many cases, however, the choice is less obvious (Figure 19.6). All of these disconnections, and reactions between the relevant Grignard reagents and ketones, should work in principle. In practice, a researcher would try them all and check the yields against costs. 

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