Hetero-Diels-Alder Reaction of Phosphorylated Nitroso Alkenes with Enol Ethers on Water: A Clean Approach Toward 1,2-Oxazine Derivatives

A concise and eco-friendly synthesis of highly fiinctionalized 1,2-oxazines from phosphinyl- and phosphonyl-nitroso alkenes has been developed. The key step of this process, which involves a two-step sequence of reactions on-water, is a regioselective hetero-Diels Alder cycloaddition reaction of enol ethers to 4-phosphinyl or 4-phosphonyl nitroso alkenes mediated by water itself. The process has also been performed under solvent-free conditions and in organic solvents for comparison.