Dual Function Catalysts. Dehydrogenation and Asymmetric Intramolecular Diels−Alder Cycloaddition of N-Hydroxy Formate Esters and Hydroxamic Acids:  Evidence for a Ruthenium−Acylnitroso Intermediate

The chiral ruthenium salen complex, 13b, functions as an efficient catalyst for the sequential oxidation and asymmetric Diels−Alder cycloaddition of hydroxamic acids and N-hydroxy formate esters. This result provides evidence for the formation of a ruthenium−nitroso formate (acyl nitroso) intermediate. The Diels−Alder precursors are prepared from simple building blocks, and the cycloadducts, bridged oxazinolactams, can serve as useful intermediates in organic synthesis.