Synthesis of pyrrolo(spiro-[2.3']-oxindole)-spiro-[4.3"]-oxindole via 1,3-dipolar cycloaddition of azomethine ylides with 3-acetonylideneoxindole.

A series of novel dispirooxindole derivatives, 3-acetyl-5-phenyl-pyrrolo(spiro-[2.3′]-1′-benzyl-oxindole)-spiro-[4.3″]-1″-benzyl-oxindoles, were synthesized via 1,3-dipolar cycloaddition of the azomethine ylide with 3-acetonylideneoxindole in high regioselectivities and yields. An unusual regioselectivity was observed in this 1,3-dipolar cycloaddition, leading to the construction of novel dispirooxindole skeleton. The substituent effects on the regioselectivity were also investigated.