Prof. László Kürti
Organic Colloquium
Department of Chemistry
Rice University
Description
Advances In the Synthesis And Application Of Strained-Ring Compounds: Catalytic & Stoichiometric Approaches
Abstract: “The synthesis of highly substituted and strained nitrogenous molecules remains a challenging task since installing substituents on small ring systems gets increasingly difficult as the degree of substitution increases. Similarly, it is difficult to install nitrogen bridges onto highly substituted and electronically diverse unsaturated systems. In this presentation a number of synthetic routes to these valuable nitrogenous building blocks will be discussed: (1) The direct and stereospecific synthesis of N-H- and N-alkyl aziridines from unactivated olefins using both transition metal-catalyzed and organocatalytic approaches that proceed through very different N-transfer processes; (2) Fully-substituted N-acyl aziridines are produced in one-pot by the reaction of N-electrophilic iminomalonates with ketone enolates – this transformation is in essence an aza-quasi-Favorskii rearrangement reaction which proceeds via a 1,2-attack followed by a low-barrier intramolecular nitrenoid-insertion into a C-C bond and (3) Structurally diverse spiro N-H azetidines are formed in a single step during the Ti(IV)-mediated reaction between oxime ethers and alkyl-Grignard reagents or via a ligand-exchange process using terminal olefins – the overall transformation proceeds via a Kulinkovich-type mechanism: a titanacyclopropane intermediate is formed and serves as a 1,2- dialkyl anion equivalent, inserting into the 1,2-dielectrophilc oxime ether substrate to ultimately give rise to the desired N-heterocyclic four-membered ring.
