Solvent-free Knoevenagel condensations and Michael additions in the solid state and in the melt with quantitative yield

摘要

Numerous Knoevenagel condensations of solid or liquid aromatic aldehydes are performed with four barbituric acids, Meldrum's acid, dimedone, cyanoacetamide, malodinitrile and methyl cyanoacetate in stoichiometric mixtures of the solids or of stoichiometric melts. The product yields are quantitative in 23 reported cases and the products do not require purifying workup. Therefore, these reactions are truly solvent-free, atom economic and sustainable and no wastes are produced. They are highly superior to less productive so-called 'solvent-free' techniques using solid supports and microwave irradiation that require solvents for removal of the support or reagents or side products. Similarly, the solution reactions generally requiring catalysts suffer from low yields and purifying workup. The new techniques provide numerous common electron-poor alkenes very easily. These are valuable building blocks for example in Michael additions. Also the latter can be quantitatively obtained in stoichiometric melts in the absence of any auxiliaries or microwave irradiation and this is demonstrated with stable and rearranging/cyclizing Michael adducts using dimedone. The quantitative yields are most easily obtained if the products are formed in the solid-state or if they crystallize directly from the melt at the reaction temperature. (C) 2003 Elsevier Science Ltd. All rights reserved. [References: 68]