Carboxylation of Active Methylene Compounds with Magnesium Thioureide-Carbon Dioxide Adducts

Abstract

Magnesium salts of ethylenethiourea [1a], 1, 3-dimethylthiourea [2 a], trimethylthiourea [3 a], 1, 3-dibutylthiourea[4 a], and 2-methylthio-2-imidazoline [5 a] captured carbon dioxide and the resulting CO2-adducts [ 1b], [2b] and [3 b] released almost quantitatively the captured CO₂ at room temperature in DMF except for [4 b] and [5 b]. The adducts [ 1b], [2b] and [3 b] transfered the CO₂ moiety easily to active methylene compounds such as indene, cyclohexanone, acetophenone, and 1-tetralone at room temperature under nitrogen atmosphere to give the corresponding carboxylic acids in good yields. However, [4 b] and [5 b] did not work effectively as CO₂ carrier. The potassium ethylenethioureide-CO₂ adduct underwent slight decarboxylation, but was ineffective as a carboxylating reagent. These experimental findings suggest that the C=S bond of the thioureas and the magnesium ion play an important role in the transcarboxylation process.