Conjugated compounds, reaction with Grignard reagents

The related 6-trifluoromethyl-l,3-dioxin-4-ones underwent conjugate addition reactions with Gilman reagents, or with Grignards with copper(I) catalysis (Eq. 112). The 6-substituted compounds were also available, and were used to synthesise threonine and aZZo-threonine analogues [303]. Stark contrast between the behaviour of fluorinated and non-fluorinated compounds is revealed in Eq. (113). While benzylmagnesium chloride adds smoothly to the 6-methyl... 

The synthetic application of organocopper compounds received a major impetus from the study of the catalytic effect of copper salts on reactions of Grignard reagents with y.,(i-unsaturated ketones.1 Whereas Grignard reagents normally add to conjugated enones to give the 1,2-addition product, the presence of catalytic amounts of Cu(I) results in... 

In an a,P-unsaturated carbonyl system, the addition could be either 1,2 or 1,4, i.e. simple or conjugate. With Grignard reagents, the nucleophilic addition can be either 1,2 or 1,4, and often depends upon any steric factors that are present in the substrate. When an a,P-unsaturated carbonyl compound is treated with a carbanion, particularly one that is stabilised by a carbonyl group, the resultant 1,4-addition with the formation of a new carbon/carbon bond is called the Michael reaction. If the reaction occurs intramolecularly, it is called the Robinson annulation reaction. 

Ordinary Grignard reagents react with a, -unsaturated carbonyl compounds and afford both 1,2-adduct and 1,4-adduct. However, methylsulfonyhnethylmagnesium bromide or p-tolylsulfonylmethylmagnesium bromide gave only 1,2-adducts in the reaction with conjugated carbonyl compounds such as crotonaldehyde, cinnamaldehyde, trans-4-phenyl-3-buten-2-one, benzalacetophenone and l,5-diphenyl-2,4-pentadien-l-one. 

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