Reactivity and Selectivity in Catalytic Reactions of Enoldiazoacetamides. Assessment of Metal Carbenes as Intermediates

Catalyst effectiveness for metal carbene formation and reactions has been surveyed using N-(tert-butyl)-3-[(tert-butyldimethylsilyl)­oxy]-2-diazo-N-(4-chlorobenzyl)­but-3-enamide in the formation of the products from both intramolecular C–H insertion and aromatic cycloaddition. Both products are indicators of metal carbene intermediates, and this system provides a means to assess catalysts for metal carbene formation. Donor–acceptor cyclopropene production from the reactant enoldiazoacetamide has been monitored to assess its formation, and the independently formed cyclopropene has also been used to assess metal carbene formation. Catalysts of rhodium­(II), copper­(I), silver­(I), Pd­(II), cationic Au­(I), and Zn­(II) convert the enoldiazoacetamide to the donor–acceptor cyclopropene which serves as the resting state for the intermediate metal carbene, and both the enoldiazoacetamide and its derivative cyclopropene give the same ratios of insertion to cycloaddition products. Catalysts of copper­(II) and ruthenium­(II) do not give the cyclopropene as an observable intermediate, and the product ratio from insertion/cycloaddition varies when the reactant is the enoldiazoacetate from that with its derivative cyclopropene. The variation of product ratio with the metal carbene precursor in copper­(II)-catalyzed reactions is dependent on the catalyst ligand, the solvent, and substituents of the benzyl group of the reactant. [Ru­(p-cymene)­Cl₂]₂ formed the products from a metal carbene intermediate with the reactant enoldiazoacetamide catalytically but with an enoldiazoacetate formed a η³-allyl ruthenium complex stoichiometrically.