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
[cyclohexane-1,3'-indoline] 3a albeit with low yields (entries 4–6 in Table 1). The spiro[cyclohexane-1,3'-indoline] 3a was clearly produced by a tri(n-butyl)phosphine-catalyzed formal [4 + 2] cycloaddition reaction. This result showed that tri(n-butyl)phosphine has a higher nucleophilic catalytic ability than
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
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Graphical Abstract
Figure 1:
Single crystal structure of compound 3l.