I. Studies on the Metal-Catalyzed Cycloadditions of Isocyanates and Unsaturated Systems and II. Chromium-Catalyzed Synthesis of 1,3-Butadienes via (Silylmethyl)allenes
Duran Galvan, Maria
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Metal-catalyzed cycloadditions of alkynes with isocyanates or nitriles are valuable tools for the synthesis of complex carbocycles and heterocycles. Although this transformation has been studied for over three decades, the cyclizations of disocyanates with 1,3-dienes or allenes are not known and the asymmetric cycloadditions of isocyanates are scarce. To expand the scope of these powerful reactions, we studied the semi-intramolecular metal-catalyzed cycloaddition of several unsaturated systems with isocyanates. Our results show that further work in this area is needed to suppress the formation of undesired homo-coupled adducts and obtain the bicyclic products in a more efficient manner. 1,3-butadienes are versatile building blocks in organic synthesis. Therefore, it is our interest to develop an efficient method for their preparation making 1,3-butadienes more available for the organic chemist. A number of methods are known for the synthesis of these compounds, but the majority of them present problems such as poor regioselectivity, low atom economy, or require the use of toxic or non-readily available reagents. In order to develop a more effective synthesis, we employed (allenylmethyl)silanes as intermediates for the preparation of 1,3-butadienes utilizing (4-bromobut 2-ynyl)trimethylsilane as a diene equivalent. A Nozaki-Hiyama-Kishi type transformation was used for the highly regioselective preparation of (trimethylsilyl)methylallenic alcohols from aldehydes and ketones. In addition, several tridentate bis(oxazolinyl)carbazole ligands were synthesized and used for the enantioselective synthesis of allenic alcohols. Carbazole ligands synthesis was achieved by the Suzuki coupling of carbazoles with different boronic acids followed by carbonylative amidation and cyclization. We report an efficient new method for the desilylation of allenic alcohols providing a variety of secondary and tertiary 1,3-butadienylcarbinols. Furthermore, our interest in extending this methodology led us to the discovery of a novel synthesis of 2-aminomethyl-1,3-dienes from N-tosyl imines.