Construction of the A-ring of cylindrospermopsin via an intramolecular oxazinone-N-oxide dipolar cycloaddition

The efficient synthesis of an A-ring synthon for the marine hepatatoxin cylindrospermopsin has been achieved. The key step features an intramolecular oxazinone N-oxide/alkene dipolar cycloaddition resulting in the establishment of the three contiguous stereogenic centers in the A-ring from one pre-existing stereogenic center in a single step.