A synthesis of spiroindolo[2,1-b]quinazoline-6,2'-pyrido[2,1-b][1,3]oxazines from tryptanthrins and Huisgen zwitterions

Abstract

The Huisgen zwitterionic intermediates, generated in situ from N-heterocycles and acetylenic esters were intercepted by tryptanthrins to afford novel spiroindolo[2,1-b]quinazoline-6,2'-pyrido[2,1-b][1,3]oxazines in CH₂Cl₂ at room temperature. Clear evidence for the structure of a derivative was obtained from single-crystal X-ray analyses. The most important feature of this reaction is the fact it forms two stereogenic centers, one of which is quaternary with remarkable diastereoselectivity.

Graphical Abstract

Keywords:

• 1,4-Dipolar cycloaddition
• Huisgen zwitterion
• 1,3-oxazines
• spiro compound
• tandem reaction