Efficient Approach to the Unknown Isoxazolo[3,4-d]thieno[2,3-b]pyridine System by Regioselective Intramolecular Nitrone Cycloadditions

An effective approach to the new isoxazolo[3,4-d]thieno[2,3-b]pyridine system was provided by way of an intramolecular nitrone cycloaddition. The required nitrones were built in good yields starting from thiophene-2-carboxylic acids. The same skeleton was achieved in optically active form employing chiral nitrones derived from N-α-methylbenzyl- and the N-α- hydroxymethylbenzyl-hydroxylamines. The absolute configuration of the products was assigned by X-ray analysis.