Download full text in PDF Opens in a new window. Article suggestions will be shown in a dialog on return to ScienceDirect. ... Please enable JavaScript to use all the features on this page. ... The 1,4-dihydropyrano[3,4-b]indolones lose CO 2 on heating to generate the corresponding indole-2,3-quinodimethanes, which can be intercepted in Diels-Alder reactions with a range of dienophiles. ... The 1,4-dihydropyrano[3,4-b]indolones lose CO 2 on heating to ...