Methylene, determination Michael

Formation of the 1 1 or 1 2 adducts is determined by the structure of the Michael acceptor. The presence of substituents on the a-carbon at the double bond favors almost exclusive formation of the 1 1 adduct. To a lesser extent, the product ratio depends both on the reactant ratio and on the amount of base. By a careful choice of conditions, either compound can be favored. The addition of a-substituted compounds containing active methylene groups to acrylonitrile or methacrylonitrile gives 1 1 Michael-type adducts. The yields are fair to good in the first case and rather modest in the second. 

The Knoevenagel condensation with 1,3-dicaibonyls followed by a Michael reaction of a second molecule of the methylene compound, with or without addition of an amine or ammonia, may be used for the qualitative and quantitative determination of aldehydes even in the presence of ketones. Thus, cyclic 3-diketones such as dimedone (59) react with aldehydes but not with ketones in the absence of a catalyst. For the characterization the bis(2,6-dioxo-4,4-dimethylcyclohexyl)methanes (67) or the 4,6-dioxo-2,2,8,8-tetramethyl-l,2,3,4,5,6,7,8-octahydro-9F/-xanthene (68) may used. ... 

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