Tri(n-butyl)phosphine-promoted domino reaction for the efficient construction of spiro[cyclohexane-1,3'-indolines] and spiro[indoline-3,2'-furan-3',3''-indolines]

• Hui Zheng,
• Ying Han,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2022, 18, 669–679, doi:10.3762/bjoc.18.68

• . Additionally, the tri(n-butyl)phosphine-promoted domino annulation reaction of isatins and ethyl isatylidene cyanoacetates produced spiro[indoline-3,2'-furan-3',3''-indolines] in satisfactory yields. Keywords: isatin; spiro[cyclohexane-1,3'-indoline]; spiro[indoline-3,2'-furan-3',3''-indoline]; spirooxindole

• employed in the reaction. However, the reaction did not proceed to give the expected spiro[cyclohexane-1,3'-indoline], while a new spiro[indoline-3,2'-furan-3',3''-indoline] was obtained, which was clearly constructed from the annulation reaction of isatin with ethyl isatylidene cyanoacetate. Therefore, we

• turned our attention to the examination of this unprecedented reaction of isatins with ethyl isatylidene cyanoacetates. At last, we successfully found that tri(n-butyl)phosphine promoted the reaction of ethyl isatylidene cyanoacetate 6a and isatin 7a always resulted in spiro[indoline-3,2'-furan-3',3