From Heteroaromatic acids and Imines to Azaspirocycles:Stereoselective Synthesis and 3D Shape Analysis

Heteroaromatic carboxylic acids have been directly coupled with imines using T3P and NEt(i-Pr)2 to form azaspirocycles via intermediate N-acyliminium ions. Spirocyclic indolenines (3H-indoles), azaindolenines, 2H-pyrroles and 3H-pyrroles were all accessed using this metal-free approach. The reactions typically proceed with high diastereoselectivity and 3D shape analysis confirms that the products formed occupy areas of chemical space that are under-represented in existing drugs and high throughput screening libraries.