A simple one-pot synthesis of 3-(aminomethylene)oxindoles was achieved by the reaction of α-azido ketones and isatylidene malononitriles via Michael addition followed by the conversion of azides to amines. All the synthesized 3-(aminomethylene)oxindoles exhibited good diastereoselectivity. α-Azido ketones constitute an important class of synthetically useful azides that exhibit double reactivity in C-C bond formation. The electrophilic carbonyl function of α-azido ketone acts as an electrophile for the attack of carbanions leading to the formation of synthetically important 2-azido alcohols. On the other hand, the active methylene group of α-azido ketones facilitates the controlled generation of carbanions followed by trapping with various carbon electrophiles that results in the formation of aldoltype products. 1 Marco and co-workers demonstrated that the reaction of α-azido ketones with highly stabilized Michael acceptors such as arylidene malononitriles leads to the formation of polyfunctionalized pyrroles via sequential 1,4-conjugate addition followed by deprotonation which induced the formation of an anion by a loss of nitrogen and intramolecular nucleophilic attack to the cyano function. 2 And also it was anticipated that α-azido ketones having a good electron-withdrawing azido moiety would provide 2-amino-4H-pyrans on reaction with arylidene malononitriles via Michael addition followed by O-ring closure. 3 Inspired by these observations, we envisioned that treatment of α-azido ketones with isatylidene malononitriles in the presence of base would form azide moiety bearing fused spiro[4H-pyranoxindole] heterocycles via Michael addition followed by O-ring closure 4 or would lead to oxospiro[indoline-3,3′-pyrrole] heterocycles via Michael addition followed by N-ring closure (Scheme 1). 2 Quite surprisingly, when we carried out the reaction of α-azido ketone 2 with isatylidene malononitrile 1 in the presence of piperidine, we observed an unexpected domino process leading to functionalized 3-(aminomethylene)oxindole derivative 5, instead of the anticipated spiroxindole derivatives 3 and 4.
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