Trivalent Phosphine-Catalyzed [4+1] Spiro-annulation Reaction Using Allenyl Imide and Methylene Cyclocompounds
Zi-Qiu Zhang1, Zhen-Kai Zhang1, Yu-Hao Wang1
1Department of Chemistry, School of Chemistry, Chemical Engineering and Life Science, Wuhan University of Technology, Wuhan 430070, China.
Abstract:
The trivalent phosphine-catalyzed [4+1] spiro-annulation reaction of allenyl imide and activated methylene cyclocompounds has been developed for the construction of various spiro-2-cyclopenten-1-ones. Oxindoles, 3-isochromanones, and 2-indanones are selected as 1C synthons to capture the in situ-generated bis-electrophilic α,β-unsaturated ketenyl phosphonium intermediate, affording the corresponding monospiro- and bispiro-cyclopentenones in good to excellent yields (≤91%) under mild conditions. The primary attempt at asymmetric catalysis using monophosphine (R)-SITCP provides promising enantioselectivity (45% ee). A plausible reaction mechanism is also proposed.
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