Benzophenones, reactions with Grignard reagents

Association between RMgX and Carbonyl Compounds Reactions of Benzophenone(s) with Grignard Reagents... 

Maruyama and associates [53] proposed three mechanisms for reactions of Grignard reagents with benzophenone, in which differentiation is introduced for the C Mg bond strength in the respective reagent (see Scheme 17). 

Such differences in mechanisms can also be derived from the results of rate measurements (Table 1) of reactions of various Grignard reagents with benzophenone, carbon dioxide, and acetone, respectively. The reactivity series of Grignard reagents toward carbon dioxide [12] is comparable with the series for acetone [13], which led to the conclusion that both types of reactions follow the same mechanistic path a concerted mechanism. Steric requirements, therefore, are not the only parameter in the predictability of results of reactions of Grignard reagents and, in fact, are of little help when no other information on the reaction mechanism is available. 

Primary amines. Copper(I)-catalyzed Grignard reaction with the reagent gives (V-substituted imines. Acid hydrolysis releases the primary amines and the bis(trifluoromethyl)benzophenone. 

In 1971 a study was made of the kinetics of the reactions of Grignard reagents with ben/ophenone using diethyl ether as the solvent 52. Included was an investigation of the products formed in the reaction. For r-bulylmagnesium chloride it was found that 50% of the product was the 1.4-dihydro-4-/-butylbenz.ophcnone. 44 4 was normal 1.2-addilion product and 69 was benzopinacol. 1.6-addilion to unstibslituied benzophenone had never been observed before, evidently because tile product easily oxidizes in air and decomposes thermally below IOO C. 

Kinetic isotope effects, which arc often a useful mechanistic tool, have been measured in several types of reactions of Grignard reagents including reactions with benzophenone. KIEs have been measured for the substitution of L1C and IJC... 

The present review will, because of the complexity of the Grignard reagents, begin with a discussion of some physical and chemical properties of the reagents. Section 1.3 is concerned with the reactions of benzophenone with Grignard reagents. This is because benzophenone has, for many years, been a favourite substrate for researchers in the field and because observations made with benzophenone are valuable for the understanding of other reactions. Section 1.4 deals with concerted reaction mechanisms with carbonyl compounds. Section 1.. ) concerns reactions with a. /3-unsaturated carbonyl compounds and Section 1.6 concerns non-carbonylic substrates which react by stepwise radical type mechanism .. 

Newer developments in the study of the reactions of benzophenone with Grignard reagents have been the use of radical probes. If the alkyl of the reagent has the ability to undergo isomerization as, for example, cyclization or cia-inms isomerization, while it exists as a free radical, it is possible to get information about the nitc of recombination of alkyl and kclyl in the formation of the various reaction products.. S-Hexenylmagnesium bromide has been used in the study of the free radical type mechanism by its reactions with oxygen and the rate of cyclization of the, S-hexenyi radical was known to he 10 s. ... 

Evidence for Radicals from Ketones and Aldehydes. In the reaction of Grignard reagents such as the bulky neopentylmagnesium bromide with benzophenone considerable amounts of benzopinacol can be formed [76] ... 

The results obtained by carrying out the usual Grignard reaction are different than that obtained in the solid state. Thus the reaction of ketone (e.g. benzophenone) with Grignard reagent (the reaction carried out by mixing ketone... 

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