Keto-enol tautomerism Michael addition

Michael addition of tin enolates to a,/3-unsaturated esters is accomplished in the presence of catalytic amount of Bu4NBr. Other typical system using lithium enolates or silyl enolates with catalysts (Lewis acid or Bu4NF) fails to give the Michael products. An ab initio calculation reveals that higher reactivity is caused by high coordination of the tin enolate and the keto enol tautomerization for Michael adducts contributes to thermodynamical stabilization (Equation (77)).231 232... 

P-Keto acids, decarboxylation, 762—763, 768, 838, 840-841, 850 Keto-enol isomerism, 355, 705—707 Keto-enol tautomerism. See Keto-enol isomerism P-Keto esters acidity of, 831 alkylation of, 839-841, 850 Michael addition of, 846—847 nomenclature of, 832 preparation of... 

The solid-state interaction of enamines (428, 333a) with trans-l,2-diben-zoylethene (87) provides quantitative yields of the pyrrole derivatives 445 or 446 [140]. These remarkable 5-cascades consist of initial vinylogous Michael addition, enol/keto tautomerism, imine/enamine tautomerism, cyclization, and elimination, all within the crystal without melting. A waste-free extraordinary atom economy is achieved that cannot nearly be obtained in solution. The milling times are unusually long here (3 h) but it s certainly worth the effort... 

The imidazolidinone-catalysed intramolecular asymmeflic Michael addition has been studied by DFT. The mechanism is identified as enamine formation followed 0 by Michael addition (which is stereochemistry determining), followed by enol-keto tautomerization and hydrolysis. 

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