Synthesis of Diastereoenriched Oxazolo[5,4-b]indoles via Catalyst-Free Multicomponent Bicyclizations

A new and highly eco-friendly approach to diverse and functionalized oxazolo[5,4-b]indoles with good yield and high diastereoselectivity (up to >99:1) has been disclosed from simple and readily available arylglyoxals with cyclic enaminones and amino acids. These microwave-assisted transformations in environmentally compatible ethanol resulted in continuous multiple bond-forming events including C-C, C-N, and C-O bonds, enabling catalyst-free multicomponent bicyclizations to rapidly build up functional N,O-heterocycles.