The major pathways for the fragmentation of dihydrosilaazaanthracenes, containing an azetidine substituent, spiro-β-lactam ring, or spirotetrahydrofuryl residue at C9 upon electron impact are related to the presence of these rings. The azetidine ring may be eliminated as a radical or by splitting "in half" to give [M-Me]+ ions. Splitting of the spiro-β-lactam ring "in half" leads to the two strongest ions M+. The loss of the tetrahydrofuryl ring leads to ions of 9-methylene- and 9-oxosilaazaanthracenes. The dlmethylsilyl group loses a methyl radical at various stages of the decomposition. © 1990 Plenum Publishing Corporation.