High Nucleophilicity of Cyclic Amidocarbene toward Aryl Isocyanates, New Approach to Spiro[azetidinone-4,3‘-indolinone] Derivatives

The nucleophilic addition of β-lactam-4-ylidenes <b>2</b>, a type of ambiphilic cyclic amidocarbene, to aryl isocyanates has been studied and their application in organic synthesis has been demonstrated. Thermolysis of spiro[β-lactam-4,2‘-oxadiazolines] <b>1 </b>in the presence of aryl isocyanates afforded both <i>N</i>-lactam and <i>O</i>-lactam substituted spiro[azetidine-2-one-4,3‘-indole-2‘-one] derivatives <b>5</b> and <b>6</b> in the total yield of 65−86%. Upon hydrolysis, products <b>5</b> and <b>6</b> were converted into spiro[azetidine-2-one-4,3‘-indole-2‘-one] <b>9</b> that was analogous to known biologically active compounds.