Diverse synthesis of pyrano[2,3-b]indol and dihydropyrano[2,3-b]indol via tunable Lewis bases catalyzed domino reactions

We first reported an example of diverse synthesis of pyrano[2,3-b]indol and dihydropyrano[2,3-b]indol from the same starting materials. In these domino reactions, we can control the reaction conditions to give three new products: pyrano[2,3-b]indol, dihydropyrano[2,3-b]indol with E or Z exocyclic double bond. Using DABCO as catalyst in THF, dihydropyrano[2,3-b]indol with E exocyclic double bond and pyrano[2,3-b]indol were obtained at room temperature and 65 degrees C, respectively. In contrast, when DMAP was selected as catalyst, dihydropyrano[2,3-b]indol with Z exocyclic double bond was formed in toluene at 80 degrees C. (C) 2015 Elsevier Ltd. All rights reserved.