Treatment of Grignard reagents with ketones

Tertiary alcohols are usually formed on treatment of ketones with Grignard reagents, as exemplified by the reaction 183 

Bergmann and Kalmus184 prepared 2-fluoro-1,1 -diphenylethanol from co-fluoroacetophenone and phenylmagnesium bromide in just that manner. 

A solution of phenylmagnesium bromide is prepared from bromobenzene (20 g), magnesium (2.5 g), and ether (50 ml) and is then treated dropwise during 15 min at 0° with a solution of co-fluoroacetophenone (14 g) in ether (25 ml). Finally a solution of ammonium chloride in ice-water is slowly added. The layers are separated and the aqueous solution is extracted three times with ether. The united ethereal solutions are dried over sodium sulfate and fractionated in a vacuum. The distillate of b.p. 70-75°/0.2 mm crystallizes rapidly and forms prisms, m.p. 71-72°, from light petroleum (yield 65%). 

Grignard reagents do not add to sterically hindered compounds instead, reduction of the carbonyl to a secondary alcohol group occurs184 provided that the Grignard organic radical has a hydrogen atom on the / -carbon atom  

In such reactions an olefin is formed from the Grignard reagent. When, however, propylmagnesium bromide is allowed to react with diisopropyl ketone, reduction to the secondary alcohol (63%) is accompanied by normal addition of the Grignard reagent to the carbonyl group with formation of the tertiary alcohol (30%) 185 and if magnesium bromide is added to the reaction mixture the yield of tertiary alcohol is considerably increased (to 65%).185 

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