10.1002/anie.201710049
Angewandte Chemie International Edition
COMMUNICATION
Based on these studies as well as literature evidences,[4,5,11]
a
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possible mechanism is proposed in Scheme 5. The active
catalyst A first forms Ru(II) complex B by eliminating two
molecules of acetic acid which might be the rate determining
step. Insertion of alkyne 2a in between C-Ru bond of complex B
affords complex C. Reductive elimination of the metal from C,
followed by carbonyl group assisted oxidative addition of the
eliminated Ru(0) into C(4o)-C(carbonyl) bond might afford
complex D.11b-c Next, decarbonylation and reductive elimination
of the metal in the presence of acetic acid affords 3aa and
regenerates the active catalyst A.
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Scheme 5. Possible reaction mechanism
In summary, we have developed a novel Ru(II)-catalyzed
decarbonylative π-insertion reaction of less strained six-
membered ring compound. This annulation reaction of 3-
hydroxy-2-phenyl chromones and di-substituted alkynes
proceeds via C-H/C-C activation, alkyne insertion and
decarbonylation reactions, providing good yields of spiro-
indenebenzofuranones which are the key skeleton of some of
the recently isolated bioactive natural products.
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Experimental Section
Typical experimental procedure:
A solution of 3-hydroxy-2-phenyl-
[8]
[9]
CCDC 1574292 contains the crystallographic data of 3fa.
chromone (1, 0.3 mmol), alkyne (2, 0.3 mmol), [RuCl2(p-cymene)]2 (5.0
mol %), PPh3 (10 mol %) and CsOAc (1.0 equiv) in tAmOH (5.0 mL) was
stirred at 85 oC under open air for 10 hours. The solvent was removed
under vacuo and the crude reaction mixture was poured into water and
extracted with dichloromethane (20 mL x 2). The organic layer was then
washed with brine and dried over anhydrous Na2SO4. The solvent was
removed under vacuo and the crude product obtained was purified by
silica gel (100-200 mesh) column chromatography using EtOAc/Hexane
(1:9) as the eluant to afford spiro benzofuranone 3.
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Acknowledgements
Authors thank SERB, New Delhi, for financially supporting us
with GPP-0303 (YSS/2014/001018) project. P. P. Kaishap
thanks UGC for the fellowship. We are grateful to the Director,
CSIR-NEIST for his keen interests.
Keywords: Decarbonylation • annulation reaction • spiro-
benzofuranone • C-H activation • ruthenium catalysis
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Ylijoki, J. M. Stryker, Chem. Rev. 2013, 113, 2244-2266; (c) Z.-X. Yu, Y.
4
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