Intramolecular cyclization of ketostabilized sulfur ylide obtained from bet
a-alanine and 2.3-pyridinedicarboxylic anhydride was studied. The structure
of the reaction product, 5-methylthio-7,8-dihydro-4,8a-diazafluorene-6,9-d
ione, was established by X-ray diffraction analysis.